Osteosarcoma is the most common type of malignant bone tumor in children and adolescents and approximately 30% of patients develop lung metastasis, which is the leading cause of mortality. In this study, we investigated the role of miR-34a in the invasion and metastasis of osteosarcoma cells by examining its expression level and functional pattern in these cells. miR-34a mimics were transfected into the highly metastatic subline, F5M2, and into the F4 subline with low metastatic potential of the paired human osteosarcoma cell line, SOSP‑9607. Cell viability patterns, cell migration and alterations in gene expression levels were assessed by real-time PCR, and changes in protein levels were assessed by immunocytochemistry and western blot analysis. The ectopic overexpression of miR-34a significantly inhibited the migration and invasive ability of osteosarcoma cells by repressing the expression of CD44. These data suggest that miR-34a plays a tumor suppressor role in the metastasis of osteosarcoma cells by repressing the expression of CD44. Of note, studies have also suggested that the CD44 protein correlates with the metastatic potential of several malignant tumors. Therefore, it can be concluded that through the inhibition of CD44 expression levels, miR-34a plays a significant role in the migration and invasion of osteosarcoma cells.