003, O03, 0O3, OO3 may mean:
- "003" - double-O 3 — fictional British agent, see 00 Agent
- 1990 OO3 - the asteroid 6131 Towen
- OO3 gauge model railway, see Modelling 3' gauge railroads
- O03 (O2) and other related blood type alleles, see ABO blood group system and ABO (gene)
- O03 Morganville Airport, see List of airports in Pennsylvania
- Tyrrell 003, 1971 Formula One season car
- BAR 003, 2001 Formula One season car
- 003 (album), by Đorđe Balašević
- BMW 003 turbojet engine
- The Adventures of James Bond Junior 003½
- Guantanamo detainee 003, see Gholam Ruhani
- 003 (UN M.49 code) for North America