<p><b>OBJECTIVE</b>To investigate the effect and mechanism of signal transducers and activators of transcription 3 (STAT-3) modulates human tongue squamous cell carcinoma invasion ability via targeting mircoRNA-21.</p><p><b>METHODS</b>Tscca and Tca8113P160 human tongue squamous cell carcinoma cell lines were used.WP1066 (STAT-3 inhibitor) , the small molecule inhibitor of STAT-3 was used to suppress the STAT-3 expression. The half maximal inhibitory concentration (IC50 value) of WP1066 in the two cell lines was determined by methyl thiazolyl tetrazolium (MTT) assay. The expression level of STAT-3 and phosphorylation of STAT-3 (pSTAT-3) was examined by Western blotting. Real-time PCR was used to detect the mircoRNA-21 expression after treated with WP1066. Matrigel matrix and transwell assay were used to determine cancer cell colony formation and invasion ability after treated with WP1066. Tumor invasion related proteins in Tscca and Tca8113P160 cell lines were measured by Western blotting. Luciferase reporter gene assay was conducted to detect the relationship between STAT-3 and mircoRNA-21.</p><p><b>RESULTS</b>The IC50 to WP1066 in Tscca cell was 3.1 and 3.5 µmol/L for Tca8113P160 cell respectively. STAT-3/pSTAT-3 protein level was suppressed significantly (Tscca: STAT-3: F = 887.154, P = 0.000; pSTAT-3: F = 332.212, P = 0.000; Tca8113P160: STAT-3: F = 322.895, P = 0.000; pSTAT-3:F = 788.357, P = 0.000). mircoRNA-21 expression was down-regulated (Tscca:F = 32.157, P = 0.000; Tca8113P160: F = 11.349, P = 0.007). The diameters of culture clone in cell treated with WP1066 were less than control groups (Tscca:F = 15.751, P = 0.004; Tca8113P160: F = 12.964, P = 0.007). The number of tongue cancer cell migrating through the transwell membrane in WP1066 treated group was less than in control groups (Tscca: F = 1688.926, P = 0.000; Tca8113P160: F = 327.528, P = 0.000). In addition, MMP-2/9 protein expression was decreased in both of the cell lines treated with WP1066, while TIMP-3 was up regulated dramatically. STAT-3 could modulate mircoRNA-21 directly.</p><p><b>CONCLUSIONS</b>Reduction of STAT-3 can inhibit tongue cancer cell invasion ability via targeting mircoRNA-21.</p>