Mercury 3 or variants may refer to:
Mercury-Redstone 3, a spacecraft of Project Mercury Mercury(III), an unknown compound of the element Mercury Mercury III, a version of the Blackburn Mercury early British aircraft Mercury III, a 1929 version of the Bristol Mercury aircraft engine
See also Mercury (disambiguation) Mercury-Redstone 3, the first U.S. human spaceflight, 1961 Mercury-Atlas 3, a 1961 unmanned space flight