PURPOSE: To retain inner pressure at molding and, at the same time, prevent burr from being torn by a method wherein a plurality of reinforcing thick parts are produced peripherally in the burr.

CONSTITUTION: A compression mold 1 for an oil seal consists of an upper mold 2 and a core bar mold 5, both of which are made into an integral body, and a lower mold 4 and a middle mold 3, both of which are made into an integral body, and has reinforcing ring 7 inserted in a cavity 6. An outer peripheral side space 9 and an inner peripheral side space 10 are divided by an annular dam 8 provided on the top face of the lower mold 4 so as to form the sealing lip 23 and the fitting part 24 of an oil seal. The burr 25 of an intermediate molded body 20 is formed by a stepped part provided on the top face, which faces to the outer peripheral, side space 9, of the lower mold 4 and a gap 12, which has the predetermined width in order to increase inner pressure, which is applied to the inner periphery of the middle mold 3. Further, a plurality of peripherally running grooves 13 having the predetermined depth C of 0.1-0.5mm are arranged at the site facing to the gap 12 on the inner peripheral face of the middle mold 3 so as to produce locally thicker parts 26 on the outer periphery of the burr 25 in order to reinforce the burr 25.