In the present study, we found that miR-124 was down-regulated in osteosarcoma cell lines and primary tumor samples, and miR-124 was further identified to be a tumor suppressor, as restoration of miR-124 expression in osteosarcoma cell lines was able to inhibit cell proliferation, promote cell cycle, and suppress cell invasion and metastasis by targeting Rac1. This evidence concerns the gene RAC1 and neoplasm.