Abstract: Interleukin 2(IL-2)activities were tested in splenocyte culture supernatant of grass carp, Ctenopharyngodon idellus and Chinese soft-shelled turtle, Trionyx sinensis under one age. IL-2 activities of grass carp and Chinese soft-shelled turtle above one age were higher than those under one age. Within 15℃ to 35℃ range,IL-2 activities of splenocyte culture supernatant of grass carp and Chinese soft-shelled turtle were the highest at 25℃,the lowest at 15℃. Thereby,IL-2 activities increased with age and depended on temperature within a certain range. However,effects of assay temperature on IL-2 activity of grass carp and Chinese soft-shelled turtle were complicated. By thymocyte(C57BL/6-8 mice)proliferation and L929 cytotoxicity assay,IL-2 activities of grass carp and Chinese soft-shelled turtle at 37℃ was higher than those at 25℃. But by thymocyte(T.sinensis)proliferation assay,IL-2 activity of Chinese soft-shelled turtle at 25℃ was higher than those at 37℃. The influential mechanism of age and temperature on immune response has been discussed.