Epoxidized eucommia ulmoides gum (EEUG) with different epoxy contents was prepared by emulsion method adopting the reaction between the carbon-carbon double bond of eucommia ulmoides gum (EUG) and performic acid generated in situ from hydrogen peroxide and formic acid. The dependence of the melting-crystallization behavior of EEUG, the vulcanization characteristics, the tensile properties, and dynamic mechanical properties of EEUG vulcanizates on epoxy content was mainly analyzed. IR and H-1-NMR results confirm the success of epoxidation reaction. With epoxy content increasing, t(10) and t(90) of EEUG/carbon black composites decrease to some extent, while M-L, M-H,M- and the difference of M-H and M-L all increase. DSC results show that the degree of crystallinity of EEUG decreases gradually to zero with epoxy content increasing, suggesting the effectiveness and uniformity of the epoxidation reaction. Interestingly, 19.6 mol% epoxy content is found to be the critical value for EUG transforming from semi-crystalline to amorphous state. Epoxidation modification leads to the decrease of hardness and tensile strength of EEUG vulcanizates, while elongation at break increases obviously. The stress-strain curves of EEUG vulcanizates confirm the alteration from rigid and hard crystalline material to soft and tough elastomer. SEM results illustrate that epoxidation modification is beneficial to improve the interfacial strength between rubber and carbon black. EEUG-19.6 vulcanizate shows increased tan delta value at 0 A degrees C while decreased tan delta value at 60 A degrees C, indicating combined improvement of wet skid resistance and rolling resistance. These should be attributed to its unique critical aggregation state between crystalline and amorphous.