The Izod impact strength of a WC [polyvinylchloride) /MOD (impact modifier) molded product was investigated by suitably reducing the amount of crosslinking agent in the rubber of MOD or by making rubber particles void when they were in the form of a latex. As a result, 1) when the amount of crosslinking agent in rubber was suitably reduced, the Izod impact strength of the PVC/MOD molded product was improved in both ordinary MOD and void MOD. However, with the extremely small amount of crosslinking agent, low Izod impact strength was exhibited. With the same amount of crosslinking agent, the void MOD showed higher Izod impact strength than the ordinary MOD. 2) SEM (scanning electron microscope) and TEM (transmission electron microscope) observations on the broken surface revealed that shear yield and crazing occurred in a whitened portion, and crazing was observed only near the surface of the broken section in a non-whitened portion. It was also found that when the crosslinking degree of rubber was reduced, cavitations were liable to be formed in rubber under stress and expanded under rubber stress in the void MOD more than in the ordinary MOD. 3) As a result of a tensile test on the molded product, it was found that the void MOD caused lower yield stress than the ordinary MOD, thereby increasing in stress concentration. 4) From these results, an estimation was carried out of the mechanism of improvement in the Izod impact strength of the MOD or void MOD using rubber with an appropriately lowered crosslinking degree.