A series of PEI/PP blends were injection molded by conventional and microcellular methods. Polypropylene (PP) was selected as the disperse phase in order to improve the cell nucleation of poly(ether imide) (PEI)/PP blends. The effect of the PP content on the morphology of the PEI/PP blends or foams, the mechanical, thermal and dielectric properties was investigated. In the immiscible PEI/PP blends, the cell density of microcellular PEI/PP foams increased greatly with the increasing of the content of PP because the surface tension effect and interface effect significantly promoted the cell nucleation in the PEI/PP blends. Meanwhile, a large amount of gaps appeared in the interface because the processing temperature of the blends was close to the starting decomposition temperature of PP, which significantly improved the PEI/PP blends toughness because of tiny spherical cells that acted as crack arrestors by blunting the crack tip.