MicroRNA-9 (miR-9) has been shown to promote the differentiation of bone marrow mesen-chymal stem cells into neuronal cells, but the precise mechanism is unclear. Our previous study conifrmed that increased autophagic activity improved the efifciency of neuronal differentiation in bone marrow mesenchymal stem cells. Accumulating evidence reveals that miRNAs adjust the autophagic pathways. This study used miR-9-1 lentiviral vector and miR-9-1 inhibitor to modulate the expression level of miR-9. Autophagic activity and neuronal differentiation were measured by the number of light chain-3 (LC3)-positive dots, the ratio of LC3-II/LC3, and the expression levels of the neuronal markers enolase and microtubule-associated protein 2. Re-sults showed that LC3-positive dots, the ratio of LC3-II/LC3, and expression of neuron speciifc enolase and microtubule-associated protein 2 increased in the miR-9+ group. The above results suggest that autophagic activity increased and bone marrow mesenchymal stem cells were prone to differentiate into neuronal cells when miR-9 was overexpressed, demonstrating that miR-9 can promote neuronal differentiation by increasing autophagic activity.