The kidney cells of grass carp (Ctenopharyngodon idellus) were exposed to 28 ℃,32 ℃,36 ℃ and 40 ℃ for 2 h or 12 h,respectively.The 28 ℃ group was taken as control.LDH leakage rates of CIK cells were determined by the trace detection of LDH kit.The cell cycles were measured by flow cytometry.The polyubiquitinylated protein was measured by dot blot,and the expressions of caspase-3 and bcl-2 genes of cells were detected by real-time fluorescence quantitative PCR.The results showed that the LDH leakage rate,the content of polyubiquitinylated proteins,and the caspase-3 expression increased significantly with the increase of incubation temperature.While the expression of bcl-2 and the cells at G0/G1 phase decreased significantly with the increasing incubation temperature.Acute thermal stress could induce the damage of cell membrane,protein,and even promote cell apoptosis.