5052 aluminum alloy were friction welded using a brake type friction welding machine. Effects of the welding conditions on axial shortening behavior and tensile strength of the friction welded joints were investigated. Upset pressure such as welding conditions were determined 1.0, 1.5 and 2.0 times of friction pressure. Burn-off length increased almost lineally just after the start of friction process. Forge length increases sharply immediately after the upset process, then, forge length reaches constant value. Total loss is a good correlation with burn-off length and forge length. In case of the upset pressure being equal to friction pressure, the tensile strength of welded joints veried very widely. If upset pressure is setting higher than friction pressure, tensile strength of welded joints become higher than that of the joint with friction pressure equal to upset pressure, and amount of scatter were reduced. The maximum tensile strength of welded joints shows 92% that of the base metal.