Interleukin-15 is a kind of formally recognized new cytokine, its cDNA sequence,function and molecular structure have been elucidated. IL-15 is similar to IL-2 in biological properties and three-dimensional configuration and its receptor utilizes the β and γchains of IL-2 receptor. Further investigation should be done on whether other unknown components participate in IL-15 receptor complexes, its detailed signaling pathway and other unknown biological activities etc.