The experiment was conducted to investigate the effects of cyclic high temperature on Ca2+ concentration and interleukin-2 (IL-2) level in lymphocyte, and T lymphocyte transformation rate and cell cycle in spleen of broiler chickens. One hundred and fifty 32-day-old Arbor Acres male broilers were randomly allotted to 3 treatments (normal-temperature group, paired-feeding group and high-temperature group) with 5 replicates in each treatment and 10 birds in each replicate. The broilers in the normal-temperature group and paired-feeding group were housed in controlled environment chambers at 22 ℃. The broilers in the high-temperature group were housed in a controlled environment chamber with daily cyclic high temperature (27 ℃—35 ℃—27 ℃), and the experiment lasted for two weeks. In addition, the broilers in normal-temperature group and high-temperature group were fed ad libitum, but the broilers of paired-feeding group were matched the diet intake of broilers in high-temperature group at the previous day of the experiment. The results showed that cyclic high temperature stress significantly increased the rectal temperature, respiratory rate and ［Ca2+］i of lymphocyte of broilers (P<0.01); after 7-d cyclic high temperature, the corticosterone (CORT) level in plasma was significantly increased (P<0.05), and the secretion of interleukin-2 in splenic lymphocytes was significantly enhnced (P<0.05), and Con A-stimulated lymphocyte transformation rate was significantly suppressed (P<0.01), and after 14-d cyclic high temperature, there was no significant difference among groups (P>0.05); flow cytometric analysis of the cell cycle indicated that the 14-d high temperature stress significantly decreased the S phase proportion of lymphocyte (P<0.01) and increased the G1 phase proportion of lymphocyte (P<0.05), but there was no significant difference in the G2 phase proportion of lymphocyte (P>0.05). These results suggested that the cyclic high temperature stress increased the concentrations of Ca2+ and interleukin-2 in lymphocyte; long-term stress exposure had a negative effect on the immune function of broilers, such as the suppression of splenic T lymphocyte transformation rate and the transition of activate T cells from the G1 phase to the S phase.［Chinese Journal of Animal Nutrition, 2010，22（5）:1243-1250］