Abstract: Objective To observe the effect of electromagnetic field(EMF) on cell immunity function.Methods After EMF exposure at the intensity of 90 mW/cm² for 20 minutes, the lymphocyte transformation rate in vivo and in vitro and the ear blubber index of delayed type hypersensitivity test were determined on the day of 3rd, 5th, and 7th.Results The phytohaemagglutinin stimulation indexes of the spleen lymphocyte in vitro were 1.15±0.05, 1.16±0.08, and 1.13±0.07, respectively, on 3rd, 5th, and 7th day after the MEF exposure, without significant differences compared with those of the control(1.09±0.03, 1.12±0.11, and 1.21±0.13), but the lymphocyte transformation rates in vivo were 43±2.1%, 53±3.0%, and 51±1.9%, respectively, and were significantly higher than those of the control(P<0.05 for all).On 3rd and 5th day after the EMF exposure, the ear blubber indexes were 2.67±0.37 mg and 2.93±0.52 mg and significantly higher than those of the control (P<0.05 for all).Conclusion Exposed to 90 mW/cm² EMF could induce cellular immune hyperfunction in mice.