Abstract: ObjectiveThe present experiment was conducted to survey the diversity of pathogenic microsporidan of Bombyx mori from the perspectives of their distribution,infectivity and taxonomic character to provide reference for effec-tive prevention of bombyx m. pebrine in sericulture.MethodThe pebrine inspection data of B. mori eggs was analyzed and the sampling inspection of B. mori was carried out to find out the distribution of pathogenic microsporidan. The infec-tivity of pathogenic microsporidan was researched according to test the semi-infection concentration(IC50),germinative infection rate and germinative infection rate of susceptible B. mori eggs. Phylogenetic tree of microsporidan was construc-ted based on SSU rRNA sequences,analysis on similarity and genetic distance was also carried out to investigate the classi-fication characters of pathogenic microsporidan.ResultThere were some diseased B. mori being infected by microspori-dan in different times and different regions,the pebrine contamination rate(poison rate)of B. mori eggs had obvious fluc-tuation. The pathogenic microsporidan all had strong ingestive infection to B. mori,such as GXM3,GXM4,GXM5, GXM6,GXM7,GXM8,GXM9,GXM10,GXM11,GXM12 and GXM13,the IC50 of most microsporidan had the same level as N.b,but there were obvious differences in the germinative infection between various pathogenic microspori-dan. The germinative infection rate of N. b was 51.67%,which was more than that of other pathogenic microsporidan. Some microsporidan had no germinative infection to B. mori,such as GXM6 and GXM13. There were eight pathogenic microsporidan that were all located in the Nosema family in phylogenetic tree,which were GXM3,GXM4,GXM5, GXM6,GXM7,GXM8,GXM9 and GXM11. They showed obvious differences in divergence and percent identity with other pathogenic microsporidan,expect that there were low divergence and high level of identity between GXM7 and GXM9,GXM3 and GXM5.ConclusionThere is wide distribution and variety for the pathogenic microsporidan of B. mori in Guangxi sericulture,and their infection had obvious differences,which means the pathogenic microsporidan of B. mori in Guangxi sericulture have rich diversity.