【Objective】To study the genetic geographical difference of Isaria fumosorosea strains isolated from different regions, and the pathogenicity of I. fumosorosea to B-biotype Bemisia tabaci.【Method】Sixteen strains of I. fumosorosea were isolated from soils of Guangdong, Fujian, and Qinghai. The bioinformatics analysis was used to identify ITS sequences similarities of the 16 strains, and the pathogenetic tree was constructed. The immersion method was employed to evaluate the pathogenicities of I. fumosorosea strains against second-instar nymphs of B-biotype B. tabaci.【Result】The ITS sequences similarities between the test I. fumosorosea strains and the reference strains(KX057373.1, KX057375.1) were over 97.7%. Nine strains from Guangdong and six strains from Fujian had no geographic difference. The ITS sequence of Qinghai strain IfTS01 was almost the same as that of reference strain (KX057375.1), and highly similar to the strain IfFJ02、IfFJ06 of Fujian and strain IfGD17 of Guangdong. The fatality rate of B-biotype B. tabaci ranged from 47% to 86% after 10 days treatment with 10 mL^–1 conidia of the 16 I. fumosorosea strains. The most effective strains, IfFJ06, IfGD02 and IfTS01, caused above 80% fatality rate of B. tabaci.【Conclusion】There is no obvious difference of genetic geography among ITS sequences of I. fumosorosea strains isolated from different areas. The pathogenicity of I. fumosorosea strains aganist B. tabaci is not related to its geographical distribution and ITS sequence similarity. There are three strains with high pathogenicity to B. tabaci，which can be used for further research.