Abstract: The effect of heat stress on the level of IL-2,IFN-γ and TNF-α in porcine serum were investigated in this study.Twelve healthy three-month-old pigs were divided into two groups at random, heat stress group and control group. The two groups were put into different AGCs(artificial climate chambers), one of which simulated high temperature in summer (the temperature changed from 26 ℃ to 39 ℃ and lasted four hours at 39 ℃ ), the other always keep at 22 ℃. The experiment lasted ten days and in the 1st, 3rd, 5th,7th and 9th day , 5 mL blood were drawn out of jugular vein soon after 39 ℃ heat stress and level of IL-2,IFN-γ and TNF-α in porcine serum was determined by using ELISA. Contrast with the control group, the level of IL-2 in porcine serum of heat stress group increased dramatically (P<0.05) on the 1st and the 3rd day after heat stress; The level of IFN-γ in porcine serum decreased dramatically (P<0.05) on the 3rd and the 5th day ; The level of TNF-α in porcine serum of heat stress group increased,but not dramatically. With the experiment going, the level of IL-2,IFN-γ and TNF-α in porcine serum of heat stress group increased or decreased gradually. On the 10th day, the level of these cytokines of the two groups was similar. The data presented indicated that heat stress restrained immune functions and the conclusion was in accordance with forepassed reports.