By comparing the difference of thermotolerance and the relationship between thermotolerance and heat shock protein (Hsp) mRNA level of two Lecanicillium lecanii strains,the mechanism of Hsp on heat stress tolerance was studied. The thermotolerance of mycelia and conidia between L. lecanii strain VL17 and VL18 were compared using mycelium growth rate method and spore germination method. Spray inoculation method was adopted to estimate the virulence of strain VL17 and VL18 against Lipaphis erysimi under high temperature stress. Realtime quantitative PCR (qRTPCR) was used to compare expression of the sHsp and Hsp70 genes. The results showed that the thermotolerance of both mycelia and conidia from strain VL18 were significantly higher than those from strain VL17. The colony diameter of strain VL18 was 63.16％ bigger than that of VL17 at 34℃ and the conidia germination rate of VL18 was 103％ higher than that of VL17 at 37℃. The insecticidal activities of the two strains against L. erysimi were significantly different when the temperature was above 31℃. The corrected mortality of L. erysimi inoculated with VL18 was 166.67％ higher than that with VL17 at 37℃. The qRTPCR analysis showed that the sHsp and Hsp70 mRNA of VL18 were higher than that of VL17 at 42℃ when the stress time was same. After a 120 min stress,expression of the Hsp70 and sHsp genes of strain VL18 were 16.97 and 63.74 folds as those of strain VL17,respectively. Furthermore,the expression of sHsp in both strains were significantly higher than those of Hsp70．In conclusion,sHsp played an important role in the response of L. lecanii to heat stress.