Abstract: Objective: To study the effect of electromagnetic radiation on immune function of mice. Methods: Two hundred and eighty-eight BALB/c mice were randomly divided into four groups,which were exposed to 2 856 MHz electromagnetic radiation at the power density of 0mW/cm²,5mW/cm²,10mW/cm² and 20mW/cm²,respectively,1h a day,for 5 consecutive days.The number of peripheral blood cells,the distribution of T-cell subpopulations（CD4 and CD8）,and thymus index were detected 1h,1d,3d,7d,15d,and 30d,respectively,after electromagnetic radiation. Results: The number of leukocytes,lymphocytes and thymus index was significantly decreased after electromagnetic radiation at any time point,while the CD4⁺/CD8⁺ ratio was increased（P＜0.05）.These abnormalities aggravated gradually with time during the study.Furthermore,the inhibitory effect of electromagnetic radiation on the immune function of mice was enhanced with the increased power density of electromagnetic radiation. Conclusion: Electromagnetic radiation can suppress the immune function of mice and the suppressing effect of electromagnetic radiation on immune function of mice increases with increasing power densities.