Abstract： Objective To study the effect of AG490 on cell proliferation and cycle of human glioma cell lines by inhibiting the STAT3 signal pathway. Methods Glioma cell lines U87 and U251 were treated with AG490, a Janus kinase (JAK) inhibitor, at different concentrations and for various durations. STAT3 and phospho-STAT3 (p-STAT3) proteins were detected by immanocytochemical staining. The blocking effect of AG490 on STAT3 signal pathway was verified by means of Western blot which displayed the expressions of STAT3 and p-STAT3 proteins in glioma cells. The cell proliferation of glioma cell lines was checked by sulforhodamine B (SRB) assay. FCM was applied to analyze the change of cell cycle. Results The expression of STAT3 was located in cytoplasm of glioma cells while p-STAT3 in the cell nucleus. The expression of p-STAT3 could be inhibited by AG490 in U251 and U87 cell lines while STAT3 stayed unchanged. And AG490 appeared to significantly inhibit the proliferation of glioma cell lines in a time-and concen ration-dependent manner. Moreover, it leads to cell cycle arrest of glioma cells in vitro. Conclusion That AG490 suppresses the cell proliferation and arrests the cell cycle of glioma cell lines in vitro indicates that the STAT3 signaling pathway plays an important role in the development of glioma. STAT3 is possible to be a promising target in the control of glloma.