The effect of friction stir welding (FSW) parameters on microstructure and properties of 15vol.%SiCp/2009Al composite welds was investigated at tool rotation rates of 400-1000 rpm for a constant welding speed of 50 mm/min. 8mm thick defect-free welds were produced at higher tool rotation rates of 600-1000 rpm, whereas an unwelded seam was distinctly visible at the root of plates at a lower tool rotation rate of 400 rpm. FSW resulted in generation of fine and equiaxed recrystallized grains of ~6 μm and significant improvement of SiC particle distribution in the weld nugget. Under as-FSW condition, the hardness of the weld nugget was significantly higher than that of as-extruded parent material. Furthermore, tensile and yield strengths of as-FSW composite welds in both the longitudinal and transverse directions were superior to those of as-extruded parent material. Post-weld T4 temper resulted in limited grain growth due to the pinning of SiC particles. Under the T4 condition, the tensile strength of the welds along the longitudinal and transverse directions reached 82 and 95% of the parent material, respectively.