In this study, the compatibility of immiscible binary blends of acrylonitrile-co-butadiene rubber (NBR) and ethylene proplylene diene rubber (EPDM) was characterized by various analytical techniques. Ultrasonic velocity measurements were conducted on solution blends of NBR and EPDM in various blend ratios as well as with the addition of either chlorinated polethylene (CM) or chlorosulphonated polyethylene (CSM) as a compatibilizer. Without the compatibilizer, the ultrasonic velocity was observed to vary in an apparently sinusoidal way with variation in the blend ratio. The addition of a compatibilizer, however, resulted in a marked increase of the ultrasonic velocity and significant changes in the nature of the plots of velocity vs. composition. Various other parameters (e.g., temperature, solid content of the solution blends, and efficacy of the compatibilizer) were found to affect the relative ultrasonic velocity values. Thermal analysis by modulated differential scanning calorimetry (MDSC) indicated that the segmental immiscibility between NBR and EPDM, and the addition of the compatibilizer resulted in characteristic peak shifts of the individual rubbers to form a broad plateau. Measurements of the storage modulus (E'), loss modulus (E ''), and tan delta properties by dynamic mechanical analysis (DMA) also showed distinctive changes. Atomic force microscopy (AFM) on the surface topography, phase images, and histogram plots of the vulcanizates of 50:50 NBR-EPDM blends were also carried out to study the effect of compatibilization.