A seal assembly for sealing a chamber formed between the radially inner and outer coaxial members spaced apart radially from each other and rotatable relative to each other comprises a first radial member extended radially inwardly from the outer member toward the outer periphery of the inner member, a second radial member disposed axially outside from the first radial member and extended radially outwardly from the inner member toward the outer member so that the first and second radial members may oppose to each other, a first seal means disposed between the tip end of the first radial member and the inner member, a second seal means disposed between a side surface of the first radial member and the second radial member, and a third seal means disposed between the outer member and the second radial member, the first, second and third seal means being so formed that leak of lubricant contained in the chamber may be permitted, while flow of foreign material from exterior may be prevented.