MPJ or mpj may refer to:
- MPJ, the IATA and FAA LID code for Petit Jean Park Airport, Arkansas, United States
- MPJ, the Indian Railways station code for Madanpur railway station, West Bengal, India
- MPJ, the NYSE symbol for Mississippi Power, an American investor-owned electric utility
- mpj, the ISO 639-3 code for Martu Wangka dialect, Western Australia