Friction stir welding (FSW) was performed on 304 stainless steel sheets. The welding speed was varied from 30 to 70mm/min. Because the FSW of thin plates is sensitive to heat input. The surface of the welds is smooth and without any macroscopic cracks and cavities only when the rotation speed is 50mm/min. The stir zone had equiaxed grains with austentic structure due to dynamic recrystallization. There was not any evidence for the presence of sigma phases being found in this study. Meanwhile, there was a weak region in the advancing side because of the flow of plastic metals. However, compared with the base material, mechanical properties of the joint are maintained in a comparatively high level.