Emerging evidence shows that microRNAs (miRNAs) act as critical regulators in the progression and chemoresistance of multiple tumors, including osteosarcoma (OS). In this study, we found that the level of miR-24 was increased in OS patients' serum, tumor tissues and OS cell lines. Furthermore, we found that knockdown of miR-24 by its specific inhibitors significantly increased the therapeutic effect of doxorubicin (DOX) on OS cell lines (MG-63 and HOS). Moreover, miR-24 inhibitors resensitized the doxorubicin-resistant MG-63 cells (MG-63/R) and HOS cells (HOS/R) to DOX. As the gene of Bcl-2 interacting mediator of cell death (BIM) was proved to be a target of miR-24 in MG-63/R cells, we further observed that the miR-24 inhibitors promoted the DOX-induced apoptosis via mitochondrial pathway. In addition, results of immunoprecipitation showed the release of second mitochondria derived activator of caspase/ direct IAP binding protein with low pI (Smac/DIABLO) abolished the biological activity of X-linked inhibitor of apoptosis protein (XIAP) by binding with it, which subsequently induced the activation of caspase 9, 7 and 3. In summary, those results strongly suggest that the miR-24-BIM-Smac/DIABLO axis might be a novel target for the treatment of OS.