In the present study, attempts have been made to modify a phenolic resin (PF) with vinyl triethoxysilane (VTES) in order to compatibilize it with EPDM. It was proved by Fourier transform infrared spectrometer (FTIR) that vinyl-silicon group had been successfully introduced to the structure of PF. Dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) were used to characterize the structure of EPDM/PF composite. Glass transition of PF disappeared and the diameter of PF phase reduced from 44 to 86 mu m to approximately 600 nm when modified PF was used. The compatibility mechanism of EPDM and modified PF is also suggested as follows: modified PF was transformed into semi cross-linked particles by condensation reaction in the presence of water and shear force of two-roll mill, and the particles were fully cured and grafted to the network of EPDM during vulcanization, respectively.