Effect of wax on ozone degradation of vulcanized rubber was investigated at temperatures between -30 and 40 . The vulcanized rubber was prepared by mixing synthetic isoprene rubber with CB, sulfur, ZnO, stearic acid, accelerator and wax, followed by heating at 160 for 8 min. It was further heated at 23 , 40 and melting temperature of each wax for 72 hours under 20% stretching, in order to segregate the wax onto the surface of the vulcanized rubber as a bleeding. Ozone exposure tests of the vulcanized rubber were carried out at the temperatures between -30 and 40 in the presence of 50 pphm ozone for 24 and 168 hours, respectively. Crack propagation of the ozone-degraded rubber was observed with a digital microscope. The wax, bleeding onto the surface of the vulcanized rubber, was found to improve the ozone resistance of the rubber as compared with an ordinary bloomed wax.