This is a complete list of senators of the Philippines during the 13th Congress of the Philippines listed by seniority from June 30, 2004, to June 30, 2007.

The criteria for seniority used in this article are derived from the cumulative length of service of a member of the Senate prior to the current Congress. Although an official roster ranking senators by seniority is not publicly available, their total cumulative years of service have been used to determine seniority. It has long been customary, following the practice of the United States Senate, to elect the most senior senator as either president of the Senate or president pro tempore, although this practice has become less common in the modern Senate. Furthermore, seniority is traditionally considered in the selection of chairpersons of major Senate committees.

In cases where senators have equal cumulative service, seniority is determined by the following criteria, in order: Longest uninterrupted period of service Earlier date on which the cumulative length of service was achieved Alphabetical order of surnames

In this Congress, Edgardo Angara was the most senior senator, having previously served 14 years in Senate, while Mar Roxas was the most junior senator.

List of senators by seniority Rank Senator Party Length of previous tenures Notes Start of Congress End of Congress 1 Edgardo Angara LDP 14 years, 0 days 2 Nene Pimentel PDP–Laban 11 years, 0 days 3 Juan Ponce Enrile PMP 10 years, 320 days 4 Rodolfo Biazon Liberal 9 years, 0 days 5 Franklin Drilon Liberal Senate president (until July 24, 2006) 6 Juan Flavier Lakas Senate president pro tempore 7 Ramon Magsaysay Jr. Lakas Liberal 8 Serge Osmeña PDP–Laban 9 Miriam Defensor Santiago PRP 10 Joker Arroyo Independent KAMPI 11 Loi Ejercito PMP 12 Panfilo Lacson Independent 13 Kiko Pangilinan Liberal 14 Ralph Recto Nacionalista Lakas 15 Manny Villar NacionalistaSenate president (from July 24, 2006) 16 Pia Cayetano Lakas Nacionalista rowspan="8" 17 Jinggoy Estrada PMP 18 Dick Gordon Lakas 19 Lito Lapid Lakas 20 Alfredo Lim PMP colspan="2" Resigned on June 29, 2007, upon taking office as Mayor of Manila. 21 Jamby Madrigal LDP PDP–Laban 22 Bong Revilla Lakas 23 Mar Roxas Liberal

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