In a rod sealing system, which comprises a buffer ring, a rod seal, and a dust seal, provided successively in this order from a fluid hydraulic side toward the outside in an annular clearance between two members in reciprocating motion, the buffer ring is made up of a thermoplastic polyurethane molding product obtained by subjecting a thermoplastic polyurethane molding product prepared by reaction of (A) a high molecular weight polycarbonatediol having a number average molecular weight Mn of 500-6,000, (B) an aromatic diisocyanate, and (C) a low molecular weight diol as a chain elongation agent in an NCO/OH ratio of 0.95-1.20,to heat treatment under conditions that a glass transition point (Tg) of hard phases becomes 170 °C or higher, preferably 170- 230 °C , and an endothermic peak area (”H) at Tg becomes 5J/g or more, by differential scanning calorimetry. The buffer ring made up of the thermoplastic polyurethane molding product has a distinguished heat resistance capable of withstanding the service environmental temperature, particularly maximum 120°C, compression set characteristics, follow-up to eccentricity, etc.