Influences of EPDM-g-MA as a compatibilizer and a phenolic antioxidant on oil and thermal aging resistance in 50/50 CPE/NR blends were investigated. It has been found that EPDM-g-MA could decrease phase size of the blend system, indicating compatibilizing effect. The optimal concentration of EPDM-g-MA is 1 phr. Beyond this concentration, phase size starts to increase. The addition of phenolic antioxidant apparently decreases the phase size in blends. This is probably due to the improvement in a thermal stabilization of NR phase in blends provided by the antioxidant, which leads to a reduction in phase coalescence during blending. In addition, the results of oil and thermal aging resistance are in good agreement with the morphological results, indicating that the oil resistance and thermal aging properties based on relative tensile strength in the 50/50 CPE/NR blends are strongly controlled by the size of the NR dispersed phase in CPE matrix. The smaller the dispersed phase size, the higher the resistance to oil and thermal aging. (C) 2004 Elsevier Ltd. All rights reserved.