The pre-heating effect was investigated of friction stir welding of A5052-H34 aluminum alloy. At first, the friction stir welding at room temperature was carried out and the distribution of temperature of specimen surface was measured in welding. Friction stir welding with heating was carried out at 150, 250, 300, 350 and 400°C, selected referred to the distribution of temperature. The joint integrity was evaluated by observation of appearances of welded part and its cross section. Good joint was obtained at temperature up to 300°C. Over 350°C, it seemed that the joint integrity had some defects due to an overplus of heat. On the other hand, the tensile strength of joints by friction stir welding with heating was close to it of non-heating one. Therefore, friction stir welding with heating would be feasible.