The compatibility for binary blends of isotactic polypropylene with rubbery ethylene-a-olefin copolymers having various alpha-olefin contents was investigated by means of differential scanning calorimetry, X-ray analysis, transmission electron microscopy, and dynamic mechanical analysis. It was found that "alpha-olefin rich" in ethylene-1-butene copolymers and in ethylene-1-hexene copolymers were miscible with amorphous polypropylene chains, when the alpha-olefin content is above 50 mol %. On the other hand, the blends with "ethylene rich" (above 50 mol % of the ethylene content) in ethylene-1-butene copolymers and ethylene-1-hexene copolymers showed a microheterogeneous morphology.