To demonstrate that miR-9 inhibits autophagy by down-regulating Beclin1 and thus enhances the sensitivity of A549 cells to cisplatin. MiR-9 inhibited Beclin1 expression by binding to its 3'UTR. The inhibition decreased the cisplatin-induced autophagy in A549 cells, evidenced by the decreased expression of LC3II and GFP-LC3 puncta and the increased expression of P62. Upregulation of miR-9 level enhanced the sensibility of A549 cells to cisplatin and increased the cisplatin-induced apoptosis. Overexpression of Beclin1 reversed above effects of miR-9 mimics, cisplatin-induced autophagy was increased and apoptosis was decreased. MiR-9 inhibits autophagy via targeting Beclin1 3'UTR and thus enhances cisplatin sensitivity in A549 cells.