Epoxidized natural rubber (ENR) was initially prepared from an in situ performic acid epoxidation reaction with 46.09 mol% epoxide groups, and the curing characteristics of the ENR/natural rubber (NR) blend with different blend ratios of ENR were studied using a Monsanto moving die rheometer. The mechanical properties of the blends, such as the tensile strength, modulus at 300% elongation and elongation at break, were also examined. The tensile strength and 300% modulus decreased with increasing ENR content and the elongation at break increased steadily with increasing ENR content. In addition, the scorch time, cure time, maximum torque and torque difference decreased with increasing ENR content. Scanning electron microscopy (SEM) of the tensile fracture surfaces of the rubber blend samples revealed better compatibility between NR and ENR with lower ENR contents. Nanocomposites based on NR/ENR blends with two different ratios, 100/0 and 80/10, reinforced with 10 phr nanosilica were also prepared to examine the effects of ENR on the mechanical properties and morphology of the nanocomposites. SEM showed that ENR assists in the dispersion of nanosilica in the NR matrix, resulting in improved mechanical properties of the nanocomposite.