Abstract: Microstructures of friction stir welding joint of 7075 aluminum alloy and H68 brass were observed by using optical microscopy(OM). The phase structure of the joint was determined by X-ray diffraction(XRD). Meanwhile, the microhardness of the welding joint was determined by microhardness tester. The results show that good weld joint is obtained when rotating speed is 1100 r/min and the welding speed is 80mm/min. 7075 aluminum alloy and H68 brass are interweaving each other with river pattern and vortexes shape, intermetallic compounds are not formed in the lap joint. The weld nugget zone is mainly composed of recrystallization equiaxed grain. Meanwhile, the grain in nugget zone is refined and the micro-hardness is increased obviously.