MK3 may refer to:
- Mortal Kombat 3, the third game in the Mortal Kombat series
- Mario Kart: Super Circuit, the third game in the Mario Kart series, released in 2001 for the Game Boy Advance
- MAP kinase kinase kinase (MK3)
- MAPK-activated protein kinase 3 (MK3)
- Mark III (disambiguation) and Mark 3