Mars 4, also known as 3MS No.52S was a Soviet spacecraft intended to explore Mars. A 3MS spacecraft launched as part of the Mars programme, it was intended to enter orbit around Mars in 1974. However, computer problems prevented orbital insertion from occurring.

The Mars program was a series of uncrewed spacecraft launched by the Soviet Union between 1960 and 1973. The spacecraft were intended to explore Mars, and included flyby probes, landers and orbiters.