By analyzing growth phenotype of the dnaJ mutant strain at 43℃, AtDjA5 and its J Domain can functionally substitute for DnaJ and its J Domain. Co immunoprecipitation experiments show that AtDjA5 can interact with DnaK. It’s speculated that AtDjA5 can stabilize the heat shock factor σ32 of E. coli and down regulate the expression of Dnak by western blot analysis. These findings suggest that AtDjA5 has a similar function with DnaJ in E. coli.