Objective:To investigate the influence on the Expression of Fas Protein of CD4 + T Cell in the cases of psoriasis by low level He-Ne laser irradiation. Methods: the expression of CD4 + T Fas protein was determined in the casee of psoriasis(n=5) pre and post-low level laser irradiation(30 min,60min and 120min)by flow cytometry as compared with the control(n=5). Results:In the cases of psoriasis,the expression of CD4 + T FAS protein 21. 4 ±3. 1% was increased significantly than that of control group 16. 8±2. 1% pre -irradiation, p<0. 05;in the control,there is no difference between pre and post- irradiation,p>0. 05;in the cases group, the expression of CD4 + T Fas protein wae positivelly corelated to the irradiation times, when the energy density arrived to 22. 92J/cm2(60 minutes)and 45. 84J/cm2(120minutes) , the expression of CD4 + T T Fas protein was increased significantly as compared with pre - irradiation, p<0. 05. Conclusion: The expression of CD4 + T FAS protein may be increased by low level He-Ne laser irradiation，therfor,the uncontrolled status of apoptosis could be corrected.