Japan competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. Japanese athletes have competed at every Summer Olympic Games in the modern era since 1912 except for two editions; it was not invited to the 1948 Summer Olympics in London for its role in World War II, and was also part of the US-led boycott of the 1980 Summer Olympics in Moscow. For the first time in its Olympic history, Japan was represented by more female than male athletes as the Japanese Olympic Committee sent a total of 306 athletes, 139 men and 167 women, to compete in 27 sports.

Japan left Athens with a total of 37 medals (16 gold, 9 silver, and 12 bronze), finishing fifth in the overall medal rankings. This was also the nation's most successful Olympics, winning the largest number of gold and overall medals in non-boycotting games and surpassing three gold medals short of the 1956 Summer Olympics in Melbourne. Ten of these medals were awarded to the athletes in judo, eight in swimming, six in wrestling, four in gymnastics, and two each in athletics and synchronized swimming. Eight Japanese athletes won more than a single Olympic medal in Athens. Japan's team-based athletes came strong and successful in Athens, as the baseball and softball teams managed to produce two bronze medals.

Among the nation's medalists were freestyle wrestlers Saori Yoshida and Kaori Icho, who both claimed their gold medals in women's wrestling for the first time, and judoka Tadahiro Nomura and Ryoko Tani, who both successfully defended Olympic titles in their respective classes. Swimmer Kosuke Kitajima became the most successful Japanese athlete in these games, striking a breaststroke double with two golds and adding a bronze to his career hardware for the team in men's medley relay. Meanwhile, synchronized swimmers Miya Tachibana and Miho Takeda managed to repeat their silver medals from Sydney in both women's duet and team routines. Takehiro Kashima, Hiroyuki Tomita, and Isao Yoneda claimed two individual medals each in men's artistic gymnastics, including their coveted gold in the team all-around.

On August 29, 2004, the International Olympic Committee stripped off Hungary's Adrián Annus hammer throw title after failing the doping test, and the gold medal was subsequently awarded to Koji Murofushi at the conclusion of the Games, making him the nation's first ever Olympic champion in the field event.

Medalists

| style="text-align:left; width:72%; vertical-align:top;"| Medal Name Sport Event Date Judo Men's 60 kg Judo Women's 48 kg Judo Men's 66 kg Swimming Men's 100 m breaststroke Gymnastics Men's artistic team all-around Judo Women's 63 kg Judo Women's 70 kg Swimming Men's 200 m breaststroke Judo Women's 78 kg Judo Men's +100 kg Judo Women's +78 kg Swimming Women's 800 m freestyle Athletics Men's hammer throw Athletics Women's marathon Wrestling Women's freestyle 55 kg Wrestling Women's freestyle 63 kg Judo Women's 52 kg Swimming Men's 200 m butterfly Judo Men's 90 kg Archery Men's individual Cycling Men's team sprint Gymnastics Men's parallel bars Wrestling Women's freestyle 48 kg Synchronized swimming Women's duet Synchronized swimming Women's team Swimming Men's 100 m backstroke Swimming Women's 200 m butterfly Swimming Women's 200 m backstroke Swimming Men's 4 × 100 m medley relay Gymnastics Men's pommel horse Emi InuiKazue ItoYumi IwabuchiMasumi MishinaEmi NaitoHaruka SaitoHiroko SakaiNaoko SakamotoRie SatoYuki SatoJuri TakayamaYukiko UenoReika UtsugiEri YamadaNoriko Yamaji Softball Women's tournament Gymnastics Men's horizontal bar Wrestling Women's freestyle 72 kg Ryoji AikawaYuya AndoKosuke FukudomeHisashi IwakumaHitoki IwaseKenji JojimaMakoto KanekoTakuya KimuraMasahide KobayashiHiroki KurodaDaisuke MatsuzakaDaisuke MiuraShinya MiyamotoArihito MuramatsuNorihiro NakamuraMichihiro OgasawaraNaoyuki ShimizuYoshinobu TakahashiYoshitomo TaniKoji UeharaKazuhiro WadaTsuyoshi Wada Baseball Men's tournament Sailing Men's 470 class Wrestling Men's freestyle 55 kg Wrestling Men's freestyle 60 kg | style="text-align:left; width:23%; vertical-align:top;"|

Medals by sportSport TotalJudo 82010Swimming 3148Wrestling 2136Athletics 2002Gymnastics 1124Synchronized swimming 0202Archery 0101Cycling 0101Baseball 0011Sailing 0011Softball 0011Total1691237

Archery

Three Japanese archers qualified each for the men's and women's individual archery, and a spot each for both men's and women's teams.

Men AthleteEventRanking roundRound of 64Round of 32Round of 16QuarterfinalsSemifinalsFinal / ScoreSeedOppositionScoreOppositionScoreOppositionScoreOppositionScoreOppositionScoreOppositionScoreRankTakaharu FurukawaIndividual64637W 146–143L 163–166Did not advanceYuji Hamano66017L 150–155Did not advanceHiroshi Yamamoto6649W 155-147W 162–154W 168–160W 111–110W 115 (10–115) (9)L 109–111Takaharu FurukawaYuji HamanoHiroshi YamamotoTeam19705colspan=2 W 254–241L 236–242Did not advance

Women AthleteEventRanking roundRound of 64Round of 32Round of 16QuarterfinalsSemifinalsFinal / ScoreSeedOppositionScoreOppositionScoreOppositionScoreOppositionScoreOppositionScoreOppositionScoreRankYukari KawasakiIndividual62237L 106–119Did not advanceSayoko Kawauchi60153W 137–129L 150–154Did not advanceSayami Matsushita62435W 165–157L 149–173Did not advanceYukari KawasakiSayoko KawauchiSayami MatsushitaTeam184714colspan=2 L 226–240Did not advance

Athletics

Japanese athletes have so far achieved qualifying standards in the following athletics events (up to a maximum of 3 athletes in each event at the 'A' Standard, and 1 at the 'B' Standard). The team was selected based on the results of the 2004 Japan Championships in Athletics.

Koji Murofushi originally claimed a silver medal in men's hammer throw. On August 29, 2004, the International Olympic Committee stripped off Hungary's Adrián Annus hammer throw title after failing the doping test. Following the announcement of Annus' disqualification, Murofushi's medal was eventually upgraded to gold.

Men Track & road events AthleteEventHeatQuarterfinalSemifinalFinalResultRankResultRankResultRankResultRankShigeru AburayaMarathoncolspan=6 2:13:115Nobuharu Asahara100 m10.331 Q10.244Did not advanceTomoaki KunichikaMarathoncolspan=6 2:21:1342Ryo Matsuda200 m24.598Did not advanceMasato Naito110 m hurdles13.565 q13.546Did not advanceRyuji Ono10000 mcolspan=6 29:06.50193000 m steeplechase8:29.076colspan=4 Did not advanceJun Osakada400 m46.395colspan=2 Did not advanceMitsuhiro Sato400 m46.706colspan=2 Did not advanceShingo Suetsugu100 m10.273 Q10.195Did not advanceToshinari SuwaMarathoncolspan=6 2:13:246Shinji Takahira200 m21.056Did not advanceDai Tamesue400 m hurdles48.803 Qcolspan=2 48.463Did not advanceSatoru Tanigawa110 m hurdles13.39 NR3 Q13.707Did not advanceTakayuki Tanii20 km walkcolspan=6 1:23:381550 km walkcolspan=6 Hiroyasu Tsuchie100 m10.375Did not advanceYuki Yamaguchi400 m46.165colspan=2 Did not advanceKen Yoshizawa400 m hurdles50.956colspan=2 Did not advanceYuki Yamazaki20 km walkcolspan=6 50 km walkcolspan=6 3:57:0016Nobuharu AsaharaShingo SuetsuguShinji TakahiraHiroyasu Tsuchie4 × 100 m relay38.535 qcolspan=4 38.494Tomohiro ItoJun OsakadaMitsuhiro SatoYuki Yamaguchi4 × 400 m relay3:02.712 Qcolspan=4 3:00.994

Field events AthleteEventQualificationFinalDistancePositionDistancePositionYukifumi MurakamiJavelin throw78.5918Did not advanceKoji MurofushiHammer throw79.553 Q82.91Daichi SawanoPole vault5.7015 Q5.55=13Takanori SugibayashiTriple jump15.9538Did not advanceShinichi TeranoLong jump7.7029Did not advance

Women Track & road events AthleteEventHeatSemifinalFinalResultRankResultRankResultRankKayoko Fukushi10000 mcolspan=4 33:48.6626Harumi Hiroyamacolspan=4 32:15.1218Mayumi Kawasaki20 km walkcolspan=4 1:37:5640Mizuki NoguchiMarathoncolspan=4 2:26:20Megumi Oshima10000 mcolspan=4 31:42.1813Naoko SakamotoMarathoncolspan=4 2:31:437Miho Sugimori800 m2:02.826Did not advanceReiko TosaMarathoncolspan=4 2:28:445

Field events AthleteEventQualificationFinalDistancePositionDistancePositionMaho HanaokaLong jump6.3134Did not advanceTakayo KondoPole vault4.1532Did not advanceChinatsu MoriShot put15.8631Did not advanceYuka MurofushiHammer throw65.3327Did not advance

Combined events – Heptathlon AthleteEvent 200 m 800 mFinalRankYuki NakataResult13.941.7611.5425.7639.752:18.46487128Points9879286318180662845

Badminton

Men AthleteEventRound of 32Round of 16QuarterfinalSemifinalFinal / OppositionScoreOppositionScoreOppositionScoreOppositionScoreOppositionScoreRankShōji SatōSinglesL 6–15, 5–15Did not advanceHidetaka YamadaL 8–15, 10–15Did not advanceKeita MasudaTadashi OhtsukaDoublesL 7–15, 17–16, 9–15Did not advance

Women AthleteEventRound of 32Round of 16QuarterfinalSemifinalFinal / OppositionScoreOppositionScoreOppositionScoreOppositionScoreOppositionScoreRankKaori MoriSinglesW 11–5, 11–4L 2–11, 4–11Did not advanceMiho TanakaL 7–11, 11–5, 8–11Did not advanceKanako YonekuraL 4–11, 7–11Did not advanceChikako NakayamaKeiko YoshitomiDoublesL 4–15, 11–15Did not advanceSeiko YamadaShizuka YamamotoL 7–15, 9–15Did not advance

Mixed AthleteEventRound of 32Round of 16QuarterfinalSemifinalFinal / OppositionScoreOppositionScoreOppositionScoreOppositionScoreOppositionScoreRankTadashi OhtsukaShizuka YamamotoDoublesL 15–13, 7–15, 13–15Did not advance

Baseball

Roster Manager: 33 – Kiyoshi Nakahata

Coaches: 31 – Yutaka Takagi, 32 – Yutaka Ohno

Preliminary round TeamWLTiebreaker611-0610-152-43-34-25-161-0160-1

Semifinal

Bronze Medal Final

Won Bronze Medal

Basketball

Women's tournament

Roster

Group play

9th-10th Place Final

Boxing

Japan sent one boxer to the 2004 Olympics.

AthleteEventRound of 32Round of 16QuarterfinalsSemifinalsFinalOppositionResultOppositionResultOppositionResultOppositionResultOppositionResultRankToshiyuki IgarashiLight flyweightL 21–26Did not advance

Canoeing

Sprint AthleteEventHeatsSemifinalsFinalTimeRankTimeRankTimeRankMiyuki ShirataWomen's K-1 500 m2:00.8607 q2:03.0767Did not advanceShinobu KitamotoYumiko SuzukiWomen's K-2 500 m1:44.7304 q1:47.6148Did not advanceMiho AdachiShinobu KitamotoYumiko SuzukiMikiko TakeyaWomen's K-4 500 m1:36.8734 q1:35.4932 Q1:40.1889 Qualification Legend: Q = Qualify to final; q = Qualify to semifinal

Cycling

Road AthleteEventTimeRankShinri SuzukiMen's road raceDid not finishYasutaka Tashiro5:50:3556Miyoko KaramiWomen's road race3:30:3041Miho Oki3:25:4220

Track Sprint AthleteEventQualificationRound 1Repechage 1Round 2Repechage 2QuarterfinalsSemifinalsFinalTimeSpeed (km/h)RankOppositionTimeSpeed (km/h)OppositionTimeSpeed (km/h)OppositionTimeSpeed (km/h)OppositionTimeSpeed (km/h)OppositionTimeSpeed (km/h)OppositionTimeSpeed (km/h)OppositionTimeSpeed (km/h)RankTomohiro NagatsukaMen's sprint10.64667.63114WithdrewToshiaki FushimiMasaki InoueTomohiro NagatsukaMen's team sprint44.35560.8723 QW 44.08161.250colspan=5 L 44.24661.022

Time trial AthleteEventTimeRankSayuri OsugaWomen's time trial35.04510

Keirin AthleteEvent1st roundRepechage2nd roundFinalRankRankRankRankToshiaki FushimiMen's keirin6 R5Did not advance

Omnium AthleteEventPointsLapsRankMakoto IijimaMen's points race13016

Mountain biking AthleteEventTimeRankKenji TakeyaMen's cross-country (1 lap)38Yukari NakagomeWomen's cross-country (1 lap)22

Diving

Japanese divers qualified two spots each in men's springboard and women's platform.

Men AthleteEventPreliminariesSemifinalsFinalPointsRankPointsRankPointsRankKen Terauchi3 m springboard456.154 Q701.795 Q690.008

Women AthleteEventPreliminariesSemifinalsFinalPointsRankPointsRankPointsRankTakiri Miyazaki10 m platform315.7812 Q486.6312 Q479.1011

Equestrian

Show jumping