Around the world, concern is growing about the amount of waste rubber going into landfills. Policymakers are encouraging researchers to find innovative ways to recycle this waste. In this study, as part of an effort to recycle waste rubber (EPDMR) as filler in compositions of EPDM, we prepare a terpolymer of ethylene–propylene–diene with 1-dodecanethiol (EPDMSDD). We use it as a compatibilizing agent to improve adhesion and incorporation of the residue (EPDMR) in EPDM/EPDMR blends. We synthesize and characterize EPDMSDD through 13C-NMR and FTIR spectroscopy. We evaluate the effect of the compatibilizer EPDMSDD using vulcanization parameters, such as optimum cure time, scorch time, and torque. To evaluate its effect on the interaction between EPDMSDD/EPDMR, we carried out mechanical tests of samples with and without EPDMSDD. Our findings show that the tensile strength and elongation increased with the addition of EPDMSDD, indicating a better interaction between EPDMR/EPDM. Tear strength also increased with the presence of EPDMSDD, particularly for the amount of 70 and 80 phr of EPDMR. This suggests a good adhesion between the phases in high amounts of waste. The micrographs of the mixtures revealed that the addition of EPDMSDD improved the dispersion of the EPDMR in the EPDM phase. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.