Abstract: Objective To investigate the potential role of miR-203 in the regulation of the proliferation and migration of osteosarcoma cells, as well as the regulatory mechanism. Methods The expression levels of miR-203 in the osteosarcoma cells and the normal osteoblasts were measured by RT-PCR. The MG-63 cell line was divided into miR-203 group transfected with miR-203 mimics, scramble group transfected with scrambles, RAB22A group transfected with pcDNA3.1-RAB22A plasmid and NC group transfected with blank plasmid by Lipofectamine 2000. The cell migration ability was measured by wound healing assay. Cell number was examined by MTT assay. The target relationship between miR-203 and RAB22A gene was predicted and verified by Target Scan software and double luciferase assay. The expression level of RAB22A mRNA was measured by RT-PCR. The expression levels of E-cadherin, N-cadherin, Vimentin and RAB22A protein were measured by Western blot. Results Compared with the hFOB cells, the expression of miR-203 was significantly low in the osteosarcoma cell lines SAOS-2, SOSP-9607, U2OS and MG-63. MTT method showed that the number of MG-63 cells in the miR-203 group was significantly smaller than that in the scramble group after cultured for 48 and 72 h (P < 0.05). After cultured for 24 h, the relative scratch area of the scramble group was significantly smaller than that of the miR-203 group (P < 0.05). TargetScan software and double luciferase assay verified the target relationship between miR-203 and RAB22A gene. The relative scratch area in the RAB22A group was significantly smaller than that in the NC group (P < 0.05). MTT method showed that the number of the MG-63 cells was significantly increased in the RAB22A group compared with the NC group after cultured for 24, 48 and 72 h (P < 0.05). Compared with the NC group, E-cadherin expression was down-regulated, N-cadherin and Vimentin expressions were up-regulated in the RAB22A group. Conclusions MiR-203 inhibits proliferation and migration of osteosarcoma cells by inhibiting RAB22A gene expression and epithelial-mesenchymal transition.