Abstract: The signal transducer and activator of transcription(STAT)proteins, which can transmit signals from extracellular to nucleus, play important roles in biological processes. The abnormal activation of STAT3 signaling pathway usually results in many malignant diseases such as tumors(leukemias, lymphomas, breast cancer and lung cancer), inflammation or immune and rheumatoid arthritis. Numerous studies have demonstrated that the activation of STAT3, which means the phosphorylation of the residue 705, can inhibit apoptosis, induce cell proliferation and angiogenesis and finally lead to malignant diseases mentioned above. In this review, the biological functions of STAT family proteins and the related diseases of STAT3 are introduced, and the inhibitors of STAT3 are summarized simply. Further development of STATs is also proposed.