Objective To explore the detrimental influence of normothermic and hypothermic cardiopulmonary by-pass during open - heart surgery on immunity function,cytokines and complements. Methods Forty patients with con-genital or rheumatic heart disease were randomized to receive the two strategies: normothermie CPB (study group) andhypothermic CPB (control group) ,20 cases in each group. Venous blood samples were collected at each time points ofpreoperation, end of CPB, day 1,4,7,14 postoperatively to examine the plasma level of IL - 2, TNF - α, C3, C4, IgG,IgM, IgA, CD3, CD4, CD8. Results IL -2 in both groups decreased significantly at day 1,4, and returned to normal atday 7 postoperatively. IL - 2 in control group was significantly lower than that in study group postoperatively. TNF - α intwo groups was all higher at time points of end of CPB,day 1,4 postoperatively;in study group,it returned to normallevel at day 7 postoperatively, whereas in control group, it was still higher at day 7 postoperatively than that before oper-ation ,and returned to normal at day 14 postoperatively. C3 in study group was significantly lower at time points of endof CPB,day 1,7 postoperatively than that in control group;C3 in both groups was all higher at time points of end ofCPB, day 1,4 postoperatively;in study group, it returned to normal level at day 7 postoperatively, whereas in controlgroup,it was still higher at day 7 postoperatively than that before operation and returned to normal at day 14 postopera-tively. CA in study group at time points of end of CPB, day 1 postoperatively was significantly lower than that in controlgroup;C4 in both groups was all lower at time points of end of CPB, day 1,4 postoperatively than that before operation.The results showed that IgA after operation in both groups was significantly lower than that before operation, and re-turned to normal at day 7 postoperatively;IgA in study group at day 1 postoperatively was higher than that in controlgroup. IgG in both group at time points of end of CPB,day 1,4 postoperatively was significantly lower than that beforeoperation. IgG in control group was significantly higher at time points of end of CPB, day 1,4 postoperatively was signifi-cantly higher than that in control group. IgM in study group was significantly lower at time points of end of CPB, day 1,4 postoperatively. In control group, IgM was significantly lower at time points of end of CPB, day 1,4,7 postoperativelyand returned to normal at day 14 postoperatively. IgM in study group was significantly higher at day 1,4 postoperativelythan that in control group. CD3 ,CD4 in both groups decreased significantly at time points of end of CPB,day 1,4,andCD3 ,CD4 in study group and CD3 in control group returned to normal at day 7 postoperatively, CD4 in control groupstill lower than that before operation at day 7 postoperatively, and returned to normal at day 14 postoperatively. CD3,CD4 in control group was significantly lower at time points of end of CPB, day 1,4 than that in study group. CD8 in bothgroups increased significantly at day 1 postoperatively ;there was no significant difference between the two groups. Con-dusions The detrimental influence of open - heart surgery under normothermic CPB on humoral and cellular immunityfunction, cytokines and complements is less than that under hypothermic CPB, so normothermic CPB is beneficial for thepostoperative recovery and anti -inflammation function.