STAT3-IN-13 (compound 6f) is a potent STAT3 inhibitor. STAT3-IN-13 has anti-proliferative effects and binds to the STAT3 SH2 domain with a K D of 0.46 μM. STAT3-IN-13 inhibits the phosphorylation of STAT3 Y705 and downstream target gene expression. STAT3-IN-13 induces apoptosis in vitro and suppresses the growth and metastasis of tumor in vivo. STAT3-IN-13 can be used for cancer research.