Effect of welding speeds is studied in Friction stir welding (FSW) using cylindrical tool for the welding of Aluminum 7075 and 5083 alloys. Sound joint of similar and dissimilar FSW were obtained by use of 20 and 45 mm/min welding speed. The temperature distribution on entire weld zone influences the grain size of FSW. The grain size at different zones, affect the properties of FSW. This study, observed that the dissimilar joining of AA7075 and AA5083 exhibits better strength at the welding speed of 20 mm/min. Similar FSW achieved better strength at 45 mm/min welding speeds. Dissimilar welding required higher heat input as compare to similar welding.