A new organic-solvent-free water-phase suspension method was used to synthesize partially epoxidized high trans-1,4-polyisoprene (TPI) to improve its properties, including oil resistance and wet-skid resistance. The epoxidation was conducted in an aqueous peracetic acid solution and on the TPI granules prepared by a bulk precipitation method with supported titanium catalyst. The effects of the synthesis conditions, including reaction temperature, reaction time, and pH value, on the epoxy content were investigated. Epoxidized trans-1,4-polyisoprene (ETPI) with epoxy contents between 10 and 80% were obtained within 4 h. Both the amorphous and crystalline regions of TPI were epoxidized. The crystallization properties decreased with increasing epoxy content. ETPIs possessed lower mechanical properties than TPI but could be enhanced by vulcanization. The oil resistance and wet-skid resistance were significantly improved after epoxidation. (c) 2007 Wiley Periodicals, Inc.