The aim of this study is to analyze the structure and morphology of epoxidized trans-1,4-polyisoprene (ETPI) obtained by water phase suspension epoxidation. With this objective, the range of epoxy group content of ETPI from 0 to 25 mol% was used. The Fourier transform infrared spectroscopy indicated that the dissoluble parts separated by ethyl acetate were epoxidized molecular chain while the insoluble parts were unreacted TPI segment. In addition, gel permeation chromatography has been used to research the change of the relative molecular weight and the the molecular weight distribution due to the effect of epoxy group content. The decrease of molecular weight states that there have small amounts of chain scission in the epoxidation reaction process. DSC data proved that the glass transition temperature raised because of the increase in rotating free energy. The decrease of ΔHm, ΔHc, and Tc indicated that crystallinity and the rate of crystallization are reduced. The mechanical properties of ETPI showed that the tensile strength and hardness reduced gradually. Finally, a morphological study of ETPI has been completed using phase contrast microscope and scanning electron microscopy. POLYM. ENG. SCI., 54:1260–1267, 2014. © 2013 Society of Plastics Engineers