A polydimethylsiloxane with an epoxide end group was grafted onto a fluoropolymer that had hydroxyl side chains by using protonic or Lewis acids as catalysts. Strong acids such as trifluoromethanesulfonic acid were found to be effective for the grafting of the polydimethylsiloxane of relatively large molecular weight (M-n 4440). A coating prepared from the graft polymer was so hydrophobic that a water droplet of 10 mu L slid down on its inclined plane surface (30 degrees with respect to the horizontal). ESCA analysis revealed that the siloxane branches are preferentially present on the surface.