Natural rubber (NR) was blended with chlorosulfonated polyethylene (CSM) with various formulation and blend ratios (NR/CSM: 80/20 -20/80, wt/wt). Rubber blends were prepared by using a two-roll mill and vulcanized in a compression mold to obtain the 2 mm-thick sheets. Tensile properties, tear resistance, thermal aging resistance, ozone resistance, and oil resistance were determined according to ASTM. Compatible NR/CSM blends are derived from certain blends containing 20-30% CSM without adding any compatibilizing agent. Tensile and tear strength of NR-rich blends for certain formulations show positive deviation from the rule of mixture. Thermal aging resistance depends on formulation and blend ratio, while ozone and oil resistance of the blends increase with CSM content. Homogenizing agents used were Stuktol (R) 60NS and Epoxyprene (R) 25. Stuktol (R) 60NS tends to decrease the mechanical properties of the blends and shows no significant effect on blend morphology. Addition of 5-10 phr of epoxidized natural rubber (ENR, Epoxyprene (R) 25) increases tensile strength, thermal aging resistance, and ozone resistance of the blends. It is found that ENR acts as a compatibilizer of the NR/CSM blends by decreasing both CSM particle size diameter and a transition temperature of CSM. (c) 2005 Wiley Periodicals, Inc.