Abstract: A method of producing an oil seal comprises the following steps: a slicing step in which a seal ring is sliced from an end of a tubular billet of a resin material in a predetermined axial thickness; a fixing step in which the radially outer portion of the seal ring is fixed in the support member; and a bending-out/thread-forming step in which the radially inner portion of the seal ring is bent out of the plane of the radially outer portion of the seal ring thereby forming a tubular seal lip, and sequentially after forming of this seal lip, a screw thread is formed on the inner peripheral surface of the tubular seal lip. The fixing step is conducted by a press having an upper die and a lower die, in which the seal ring is fixed in the support member.