Abstract: The temperature fields in inertial friction welded bars, rotating and slipping ones, were measured by thermocouple and wireless temperature-measuring system. The asymmetry of the temperature distribution at both sides of inertial friction interface was investigated. The geometrical feature and macrograph of inertial friction welding zone under different welding conditions were statistically analyzed. It is shown that the temperature and its rising rate at the slipping side are higher than at that one at the rotating side. The axial shortening quantity, flash width and the width of thermal mechanical affected zone(TMAZ) at the slipping side are greater than that one at another side. It is considered that the asymmetry of temperature distributions at both sides of inertial friction interface is closely relevant to the asymmetry of geometrical feature at both sides of the inertial friction welding zone.