Abstract: Objective To explore the effect of low dose X-ray irradiation on cell immuno-function of BALB/C mouse.Methods The mice were divided in to three groups and exposed to 0,2,and 3Gy X-ray,respectively.Then T cell subsets and natural killer(NK)cell were examinde with FACS every week for five weeks.Results One week after 2Gyirradiation,the CD₃⁺,CD₄⁺,CD₈⁺,CD₁₆⁺ CD₅₆⁺ cells in peripheral blood were 24.76±1.87,22.87±1.71,1.07±0.07,4.64±0.78(P<0.05)with progressive decrease and recovered in the fourth week.One week after 3Gyirradiation,the CD₃⁺,CD₄⁺,CD₈⁺,CD₁₆⁺ CD₅₆⁺ cells in peripheral blood were 4.11±0.21,2.33±0.91,0.17±0.07,2.33±0.18(P<0.01)with progressive decrease and recovered in the fifth week.The decrease of subsets cell was more obvious in miceirradiated with 3Gy than that of the mice with 2Gy irridiation(P<0.05).Conclusion Cell immuno-function of BALB/C mouse declined obviously after low dose X-ray irradiation and recovered gradually after 4-5 weeks.