The Friction stir welding (FSW) is a new, promising and effective welding process to weld the materials which are difficult to weld by conventional fusion welding process. Welding parameter plays a significant role in defining the quality of weld. The right choice of the welding parameters will result sound welds and which improves the mechanical properties of material. Radiography and ultrasonic testing are very effective way to detect and assess flaws or harmful defects without change of the usefulness or serviceability of materials. In this paper, Aluminum AA-5083 is welded by FSW technique with variation in rotational and transverse speed of tool. The radiography and immersion ultrasonic testing was performed on the welded material for detecting various defects. It is found that as the transverse speed increases, the generation of heat input decreases which is causing the cavity or groove like defects. © 2011 IEEE.