Mercury-Atlas 4 was an unmanned spaceflight of the Mercury Programme. It was launched on September 13, 1961 at 14:09 UTC from Launch Complex 14 at Cape Canaveral, Florida. A Crewman Simulator instrument package was aboard. The craft orbited the Earth once.

This flight was an orbital test of the Mercury Tracking Network and the first successful orbital flight test of the Mercury Programme. (All previous successful launches were suborbital.) The payload consisted of a pilot simulator (to test the environmental controls), two voice tapes (to check the tracking network), a life support system, three cameras, and instrumentation to monitor levels of noise, vibration and radiation. It demonstrated the ability of the Atlas LV-3B rocket to lift the Mercury capsule into orbit, of the capsule and its systems to operate completely autonomously, and succeeded in obtaining pictures of the Earth. It completed one orbit prior to returning to Earth. The capsule was recovered 176 miles east of Bermuda. One hour and 22 minutes after splashdown the destroyer USS Decatur (DD-536) (which was 34 miles from the landing point) picked up the capsule. On the MA-4 mission, all flight objectives were successfully achieved.

The mission used Mercury spacecraft # 8A (which had also been launched on the aborted MA-3 mission as spacecraft # 8) and Atlas # 88-D.