In this study, the blending system of natural rubber (NR) and silicone rubber (SR) at 70/30 ratio was investigated. Two kinds of graft polymers, polysiloxane-g-octane with different grafted ratios (polymers A, B, and C) and polysiloxane-g-(3,7-dimethyl-6-octylene) (polymer D), were designed and synthesized to serve as compatibilizers. Dynamic mechanical analysis and scanning electron microscopy analyses showed that the compatibilizers improved the compatibility between NR and SR, and resulted in improved mechanical properties. For example, the tensile strength of the blends with compatibilizer C was 11.7 MPa, whereas that of the blends without any compatibilizer was only 7.86 MPa. The larger the grafted ratios, the better the compatibilization effect of the graft polymer. The differences in compatibilization effects between non-reactive (polysiloxane-g-octane) and reactive [polysiloxane-g-(3,7-dimethyl-6-octylene)] compatibilizers can be attributed to their different chemical compositions. The crosslink density obtained from solid-state nuclear magnetic resonance indicated that the reactive compatibilizer (polymer D) engaged in the crosslink reaction through the active vinyl at the side chains, which effectively inhibited the decreasing trend of the crosslink density caused by the addition of compatibilizers. POLYM. ENG. SCI., 54:355-363, 2014. (c) 2013 Society of Plastics Engineers