Polypropylene (PP) and Nylon6 were extruded with a single screw extruder. Nylon6 could form microfibrils in a PP matrix. When the blends were compression-molded at the temperature between the melting temperature of PP and that of Nylon6, these fibrils could be maintained in the matrix. The existence of Nylon6 microfibrils could improve the impact strength, but the tensile strength of the composites decreased. Differential scanning calorimetry (DSC) analysis show that Nylon6 microfibrils could affect the crystallization of PP slightly.