The kit uses a double-antibody sandwich enzyme-linked immunosorbent assay (ELISA) to assay the level of Rat Interleukin 2(IL-2) in samples. Add Interleukin 2(IL-2) to monoclonal antibody Enzyme well which is pre-coated with Rat Interleukin 2(IL-2) monoclonal antibody, incubation; then, add Interleukin 2(IL-2) antibodies labeled with biotin, and combined with Streptavidin-HRP to form immune complex; then carry out incubation and washing again to remove the uncombined enzyme. Then add Chromogen Solution A, B, the color of the liquid changes into the blue, And at the effect of acid, the color finally becomes yellow. The chroma of color and the concentration of the Rat Substance Interleukin 2(IL-2) of sample were positively correlated.