In this paper the Ficoll method was used to isolate peripheral blood lymphocyte of rats, and then the isolated lymphocytes were treated by heat shock for 90 min under 42 ℃ and 5 % CO,2,. Flow cytometer was applied to detect the expression of HSP70 after heat shock treatment at different revival time. Flow cytometry Annexin V/PI was utilized to measure the apoptosis rate of lymphocytes which were already pretreated by heat shock and irradiated under 0.5 Gy, 1.0 Gy, 1.5 Gy, 2.0 Gy ,2.5 Gy, 3.0 Gy X-ray. The expression of HSP70 after heat shock treatment and the influence of HSP70 to the apoptosis rate of lymphocytes irradiated under different doses has been investigated. The results show that the expression of HSP70 in lymphocytes increases obviously at 1h and reaches the maximum at 4 h after heat shock treatment, and can maintains in 24 h. The expression of HSP70 induced by heat shock pretreatment can counteract lymphocyte apoptosis produced in irradiation by X-ray (1.0~3.0 Gy). So the irradiation by X-ray is a useful method to confirm counteraction of lymphocyte apoptosis by HSP70.