Abstract: 【Objective】This research was aimed to understand the genetic polymorphism and evolving characteristic of the gp64 genes derived from Bombyx mori nucleopolyhedrovirus(BmNPV) in Guangxi, study the condition of Bm-NPV epidemic and spread in Guangxi sericultural regions, andreveal the patterns and mechanisms of maintaining genetic diversity in BmNPV population.【Method】The gp64 gene of 20 Guangxi BmNPV strains were sequenced and analyzed.The phylogenetic tree was constructed according to gp64 gene and the epidemic distribution map was drawn.The pathogenicity of different strains was also compared.【Result】The open reading frame(ORF) length of gp64 genes of these Guangxi BmNPV strains showed three conditions(1590, 1593 and 1599 bp), which encoded GP64 proteins of 529, 530 and 532 amino acid residues, respectively.The homologies of nucleotide sequence in gp64 genes of 20 Guangxi BmNPV strains was 97.6%-99.2% and the homologies of deduced amino acid sequence was 96.4%-99.6% compared with standard reference T3 strain.The mutations of GCG deletion and GC/TGCCG insertion were found near the N terminal of gp64 gene of Guangxi BmNPV strains.The site mutation numbers of nucleotide substitution were between 13 to 28, but most of them were synonymous substitutions which had little effect on the trimeric spatial conformation of the coded protein.There were three to four N-glycosylation sites in decoded amino acids of gp64 genes of Guangxi BmNPV strains.There were two O-glycosylation sites in all strains except for GXZSand the predicted sites were all the same.Almost all the Guangxi BmNPV strains were clustered as CladeⅠwhich was further separated into two major groups(Sub-clade I and Sub-clade II) in the phylogenetic tree constructed based on gp64 gene, while almost all the reference strains from abroad were clustered as CladeⅡ.The BmNPV epidemic distribution showed coexistence of concentration and scatteration.The median lethal dose(LD₅₀) of GXUA strains for 4^th and 5^th instar silkworm were 3.3 and 3.1, while LD₅₀ of GXUA strains for 4^thand 5^th instar silkworm were 5.5 and 5.3.It indicated that BmNPV strain with less glycosylation site in GP64 protein glycosylation site showed weak pathogenicity.【Conclusion】A major mutation in signal peptide of gp64 genes of Guangxi BmNPV strains occurs, frequency of synonymous mutation is high and a relatively independent cluster is formed during the evolution.The diverse pathogenicity of BmNPV strains may be related to the differentiation of GP64 protein glycosylation sites.It shows that there are diverse genotypes and phenotypes among the Guangxi BmNPV strains.These diversities sustain the genetic diversity in BmNPV wild population to a certain extent.