This paper analyzed the effect of ribs on the breakdown characteristics when a metallic particle attaches on the various spot of GIS spacer, using electric field analysis. Also, it was compared with the experimental result of breakdown voltage characteristics for the spacer with a metallic particle on its various spot and with the shape, the length, and the thickness of the ribs varying. The results of electric field analysis show that the electric field concentration of the rib is more weakened than other parts and therefore it restrains the proceeding of streamer, which occurs at the breakdown. And it is verified through experiments that the breakdown voltage of the spacer with rib is higher than that of the spacer without rib. The breakdown characteristics depend on the shape, the length, and the thickness of the rib as well. Also, it is confirmed by the electric field analysis and the experimental results that the electric breakdown characteristics could be improved by rounding the rib edge.