DIII can refer to:

In general 503 (number) in Roman numerals AD 503 (), a year in the Common Era

Transportation Mercedes D.III aircraft engine City of Detroit III (known as "D-III"), a Great Lakes and Detroit River passenger paddle steamer

Aircraft Albatros D.III, a 1916 German biplane fighter aircraft Fokker D.III, a 1916 German single-seat fighter aircraft Phönix D.III, a variant of the Austro-Hungarian First World War Phönix D.I biplane fighter Pfalz D.III, a 1917 German fighter aircraft Schütte-Lanz D.III, a 1918 German fighter aircraft prototype Siemens-Schuckert D.III, a 1917 German prototype single-seat fighter aircraft

Other uses DIII-D (tokamak), a tokamak located in San Diego, California, US Diablo 3 (stylized: Diablo III), a 2012 videogame

Division 3 (disambiguation)

See also

503 (disambiguation), "diii" when written in Roman numerals D3 (disambiguation)