Hydrophilic microparticle and nanoparticle-filled isotactic polypropylene (iPP) composites containing 5 wt% particles were extruded in a Berstorff extruder and then injection molded. For characterization the tensile and unnotched Charpy impact tests were performed. The results show that significant improvements in tensile strength, yield elongation, and unnotched impact strength are achieved in iPP/nanoparticle composite based on a good dispersion quality of nanoparticles. In the case of iPP/microparticle composite, the tensile modulus and yield strength are markedly increased compared to neat matrix, but the yield elongation and unnotched impact strength are drastically decreased due to broad size distribution of microparticles. The fracture mechanisms were discussed by studying surface morphology of failed samples. Furthermore, the influence of crystalline behavior on mechanical properties of iPP composites was discussed.