JAK/STAT pathway is a cytokine-stimulated signaling, which is also known as the IL-6 signaling pathway. The JAK family has four isomers namely, JAK-1, JAK-2, JAK-3, and tyrosine kinase-2 (TYK-2). Other components of the signaling are STATs, which are responsible for the transducing signal and activation transcription. So, this pathway directly modulates signaling from receptors to the nucleus, followed by a highly organized dynamic process. It regulates various functions of the body and plays a fundamental role in various conditions such as immune regulation, hematopoiesis, cell differentiation, proliferation and apoptosis. Therefore, JAK/STAT signaling cascade has become an important drug target for inflammatory and neoplastic diseases, and hence a number of small molecule agents so called jacinibs have been developed recently. Accordingly, the first jakinibs approved for human uses are tofacitinib, which inhibits JAK-1/JAK-2/JAK-3 for the treatment of a rheumatic disease, i.e., rheumatoid arthritis; however, ruxolitinib, a JAK-1/JAK-2 inhibitor, was the first agent to receive approval, as a treatment for myeloproliferative neoplasms.