Abstract: Dissimilar metals of TC1/LF6 were lap jointed by friction stir welding(FSW) and the microstructure of the lap joint was studied. The results showed that good appearance of weld joint without defects such as cavitation and crack was obtained when the rotation speed of stir head was 1500 r/min and the welding speed was 60 mm/min. Ti alloy and Al alloy intensively mix and form nugget zone in the lap zone. Ti alloy which is stirred into Al alloy on both sides of the nugget bends under the extrusion effection of the pin and tight couples with Al alloy. The microstrucrure in the interfacial zone of the lap joint center is lamellarstructure and can be divided into three layers. The layer closed to the nugget zone and TC1 base metal is black and white stripped structure which contains Ti-Al intermetallic compound generated during FSW. The layers in the center are black lamellar structure and stripped structure with black particles distributing on the gray matrix. Black lamellar structure is TC1 base metal which is stirred into the interfacial zone, and the stripped structure with black particles distributing on the gray matrix is mechanical mixture of TC1 base metal and LF6 base metal.