Abstract: To study the relationship between the HSP70 overexpression and the thermotolerance of cells.The HSP70 of K₅₆₂ cells were induced by CdSO₄ and the level of HSP70 were detected by RTPCR,we observed the effects of HSP70 to the heat resistanceby MTT.One hour after the CdSO₄ affected the cells,the HSP70 of cells increased much more,the heat resistance ability of the HSP70 high cells were much more strong than that of the HSP70 low cells and there was a positive correlativity between the HSP70 and the heat resistance.The overexpression of HSP70 that induced by chemical factor could enhance the ability of thermotolerance of cells.