Abstract: In order to study the effect of avian pathogenic Escherichia coli O₇₈ on the serum cytokine levels of Bian chicken, 112 30-day-old Bian chickens were divided into 2 groups. 7 treatments were in the control group, 8 chickens in each treatment, by intraperitoneal injection of sterile saline; and 7 treatments were in the test group, 8 chickens in each treatment, by intraperitoneal injection of avian pathogenic E. coli O₇₈ suspension of 50% lethal concentration. The test period was 7 days; at 0,0.5,1,1.5,3,5,7 d 7 different time points, the clinical symptoms, number of deaths, serum cytokine immunoglobulin, interleukin（IL）,interferon-γ（IFN-γ） and tumor necrosis factor-α（TNF-α） levels of chickens infected with avian pathogenic E. coli O₇₈ were detected by observation recording method and enzyme-linked immunosorbent assay（ELISA）. The results showed that the chickens in the test group infected with avian pathogenic E. coli O₇₈ on the first 0.5 to 1.5 days showed clinical symptoms; the clinical symptoms were severe on the 1.5 to 3 days, and some chickens died; on the 3 to 5 days, the number of chicken deaths increased but the mental state of the undead chicken had improved; there were no dead chickens on the 7 th day, and the overall condition of the Bian chickens returned to normal. The immunoglobulin levels of the test group on day 1,1.5,and 3 were extremely significantly lower than those of the control group（P＜0.01）;the levels of IL-2,IL-4,and IL-6 on day 1,1.5 were extremely significantly higher than the control Group（P＜0.01）;the levels of IL-8,IL-10,IFN-γ,and TNF-α on day 1,1.5,and 3 were significantly higher than those of the control group（P＜0.01）. The immunoglobulin levels of the test group continued to decrease on day 0.5-1.5,and dropped to the lowest level on day 1.5, and gradually increased from day 3;IL-2,IL-4,IL-6,IL-8,IL-10,IFN-γ,and TNF-α levels continued to increase on day 0.5-1.5, and reached the highest level on day 1.5,and gradually decreased from day 3. The results indicated that the clinical symptoms of Bian chickens were infected with avian pathogenic Escherichia coli O₇₈ on the 0 th to 7 th days. The levels of serum cytokine, immunoglobulin first decreased and then increased, while the levels of interleukin, IFN-γ and TNF-α first increased and then decreased. The infection was the most serious on day 1.5,and it started to recover after the third day.