[Abstract] Objective: To analyze the expression of miR-185 and cell division cyclin 42 (CDC42) in osteosarcoma tissues and cells, and to preliminarily explore whether miR-185 affects the proliferation and migration of osteosarcoma MG63 cells by regulating CDC42. Methods: The cancer tissues and para-cancerous tissues of 28 patients with osteosarcoma that pathologically confirmed in the Fourth People's Hospital of Hengshui City from January 2020 to January 2021 were collected for this study. Immunohistochemistry was used to detect the expression of CDC42 in osteosarcoma tissues, and qPCR was used to detect the expression of miR-185 in osteosarcoma tissues. Dual-luciferase reporter gene experiment was applied to verify the targeting relationship between CDC42 and miR-185. According to different transfectants, MG63 cells were divided into miR-185 mimic group, miR-NC group, miR-185 inhibitor group, NC-inhibitor group, CDC42 group (transfected with CDC42 over-expression vector), and negative control (NC) group. The effects of miR-185 and CDC42 expression on the migration, proliferation and cell cycle of MG63 cells were detected by scratch healing assay, CCK-8 method and FCM, respectively. A nude mouse xenograft model was constructed by inoculating osteosarcoma MG63 cells. Immunohistochemistry, qPCR and WB methods were used to detect the effects of over-expression or knock-down of miR-185 on the expression of Ki67 and CDC42 in transplanted tumor tissues. Results: Compared with para-cancerous tissues, the expression of miR-185 in osteosarcoma tissues was significantly decreased, while the expression of CDC42 was significantly increased (all P<0.01). CDC42 was verified to be a target gene of miR-185. Compared with the control group, the migration and proliferation of MG63 cells in the miR-185 mimic group were inhibited (all P<0.01), while the migration and proliferation of MG63 cells in the CDC42 group were increased and the cell cycle was arrested in the S phase (all P<0.01). Compared with the miR-185 group, the migration and proliferation abilities of MG63 cells in the miR-185+CDC42 group were promoted, and the proportion of cells in S phase was increased (all P<0.01). Compared with the control group, the expression of Ki67 and CDC42 in the transplanted tumor tissues of miR-185 mimic group was significantly decreased (all P<0.01), while the opposite results were observed in miR-185 inhibitor group (all P<0.01). Conclusion: miR-185 is lowly expressed while CDC42 is highly expressed in osteosarcoma tissues. miR-185 can inhibit the proliferation and migration of osteosarcoma MG63 cells by negatively regulating the expression of CDC42.