The miscibility of polychloroprene rubber (CR) and ethylene-propylene-diene terpolymer rubber (EPDM) was studied over the entire composition range. Different blend compositions of CR and EPDM were prepared by initially mixing on a two-roll mill and subsequently irradiating to different gamma radiation doses. The blends were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, density measurement, hardness measurement, and solvent permeability analysis. The compatibility of the blends was Studied by measuring the glass transition temperature and heat capacity change of the blends. The immiscibility of blends was reflected by the presence of two glass transition temperatures; however, partial miscible domains were observed due to inter diffusion of phases. Permeation data fitted best with the Maxwell's model and indicated that in CR-EPDM blends, EPDM exists as continuous phase with CR as dispersed phase for lower CR weight fractions and phase inversion Occurred in 40-60% CR region. It was observed that CR improved oil resistance of EPDM, however, the effect was prominent for blends of >20'% CR content. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3552-3559,2008