In our early studies, the abnormal shape of the polyhedra of Bombyx mori nuclear polyhedrosis virus (BmNPV) induced by chemical mutagenesis were occurred, and the genome of the mutated BmNPV obtained from the successive test had some change in the restriction endonuclease partners of EcoRⅠ、BglⅡ and BamHⅠ. The present studies showed that the arrangement of the crystal lattice of the polyhedrin was disorderly, and the SDS-PAGE electropherogram of the polyhedrin depicted distinct change in comparison with control group. The results of sequencing analysis on the polh gene showed that the many point mutations with characteristics of the base substitution had occurred at some sites of the BmNPV polh gene in three mutated groups, and these results more revealed (exposed) molecular mutagenesis of the mutagens above those to BmNPV.