Abstract: Titanium alloy and aluminum alloy are good for the structure materials in the fields of aerospace and aviation because of their excellent properties. It is necessary to join these two materials for wider applications. TC4 titanium alloy and L5 pure aluminum are joined by friction welded and then post-welding tempering treatment have been conducted. By means of the optical microscope detecting, EDX analysis, micro-sclerometer and tensile test, we explore experimentally the microstructure characteristics and diffusion behavior of the friction welded joint of TC4 titanium alloy and L5 pure aluminum. As expected, there are good friction weldability between TC4 titanium alloy and L5 pure aluminum and no intermetallic phases created in friction welding zone under the welding parameters used in this trial.Furthermore, the tensile strength of the welded joint exceeds that of the base metal aluminum.After post-welding heat treatment, the diffusion zone of main alloying elements Ti, Al and V widens and the microhardness of the friction welded joints near titanium increases greatly because of the aging effect.