AIM:To investigate the effects of down-regulated miR-9 expression on the proliferation , invasion and migration of nasopharyngeal carcinoma (NPC) cells.METHODS:Human NPC CNE1 and CNE2 cells were transfect-ed with the inhibitor of miR-9 by Lipofectamine to down-regulate the expression of miR-9, and the cells transfected with an inhibitor control were also set up .The cell proliferation and cell cycle were evaluated by CCK-8 assay and flow cytometry . The cell invasion and migration abilities were detected by Transwell invasion and wound -healing assays .Immunoblotting was applied to analyze the levels of the proteins .RESULTS:Compared with control group , inhibition of miR-9 expression in the NPC cells by transfection of the miR-9 inhibitor significantly decreased the proliferation ability (P<0.05).The per-centages of the cells in G 0/G1 phase [ CNE2: ( 57.96 ±1.39 )% vs ( 47.93 ±1.76 )%, P<0.05; CNE1: ( 51.24 ± 0.88)%vs (48.29 ±0.39)%, P<0.05] were significantly increased.The migration distances [CNE2: (186.50 ± 7.94)μm vs (247.56 ±15.56)μm, P<0.05;CNE1:(139.06 ±16.73)μm vs (230.66 ±14.27)μm, P<0.01] and the invasion ability of the CNE2 cells (43.00 ±3.17 vs 65.80 ±5.20, P<0.01) were also significantly inhibited .Moreo-ver, the tumor cells transfected with the inhibitors produced lower β-catenin.CONCLUSION:Inhibition of miR-9 expres-sion suppresses the proliferation , invasion and migration of nasopharyngeal carcinoma cells .