Miscibility for blends of isotactic polypropylene (PP) and ethylene-d(4)-propylene random copolymer (EPR)s prepared by copolymerization of propylene and perdeuterated ethylene with metallocene catalyst has been investigated by small-angle neutron scattering (SANS). SANS experiments were conducted for the blends of PP with EPRs containing 19 mol % (D-EPR19) and 47 mol % (D-EPR47) of deuterated ethylene unit at various temperatures. SANS results indicated that most of the blends are in the homogeneous one-phase mixture, and the Flory-Huggins interaction parameter chi analyzed by the random phase approximation is approximately 5.0 x 10(-3) for the PP/D-EPR47 blend while it is very small and within the range -1.0 x 10(-3) less than or equal to chi less than or equal to 1.0 x 10(-3) for the PP/D-EPR19 blend. It was also revealed that chi does not change with temperature meaningfully within the temperature range 440 less than or equal to T less than or equal to 482 K, while phase separation due to crystallization of PP vias observed at 373 K. No domain structure of EPR whose size is in the range of an optical microscope was observed by TEM for the blends quenched from the melt.