The crystal structure of Mn3Ga has been determined by means of the X-ray powder method. The unit cell is hexagonal, with a = 5.4065?, c = 4.3537?, and c/a = 0.8053 at 20℃ for the alloy containing 26.8 at. % Ga. The space group is D6h4-P63/mmc. Each unit cell contains two formula units, the six Mn atoms being situated at the 6(h) positions with xh = 0.837, and the two Ga atoms at the 2(c) positions. It is a deformed form of the DO19 type close-packed ordered structure. The homogeneity range corresponding to this structure in the Mn-Ga system does not include the ideal composition however, but is displaced to the Ga-rich side.