Abstract: Objective In order to explore the effect of low dose γ- radiation or cigarette smoking and their combined effect on the synthesis of protein and heat stress protein(HSP70) of embryonic brains of mice.Methods Protein and HSP70 in embryonic brains of mice were determined with Lowrey method and western dot bloting following low dose γ-radiation(⁶⁰Co,0-1.0Gy)and cigarette smoking(0-2.0 cigarette/mouse) exposure.Results Protein in embryonic brains of mice of the 0.5Gy group、1.0Gy group and high concentration group(2 cigarette/mouse) were lower than that of the control,meantime the significant combined effect of low dose γ-radiation and cigarette smoking was found.The results also showed that HSP70 increased significantly in embryonic brains of mice exposed to low dose γ-radiation and cigarette smoking,and the increase of HSP70 in embryonic brains of high dose γ-radition group and high concentration cigarette smoking group was less than low dose γ-radiation group and low concentration cigarette smoking group,and embryonic brains HSP70 in the mice of combined effect group was decreased compared with the single γ-radiation group.There was dose dependent relationship in γ-radiation and cigarette smoking group.Conclusion The results indicated that the low dose γ-radiation or cigarette smoking and their combined effect may cause low protein of embryonic brain and induced the synthesis of HSP70.The results suggested that there was relationship between the damage of emlbryonic brain and the synthesis of the protein and HSP70.