It has been shown that the mechanical properties of NR/BR/EPDM blends can be improved by using APPS as a modifier. In this paper, it is demonstrated that modification of EPDM with APPS takes place and saturation occurs when the APPS amount reaches 5 wt.-%. It is shown that the rubber/carbon black affinity improves by using APPS-grafted EPDM in the blend. TEM and STEM images clearly show that the NR/BR/APPS-EPDM blend contains a significantly higher content of homogeneous rubber phase than the unmodified NR/BR/EPDM blend. The much better distribution of the carbon black in the APPS-EPDM phase is considered the main reason for the improvement in properties of the blend.