Third generation bisphosphonates (BPs), including YM175 and YM529, are known to inhibit bone resorption. The aim of this study was to evaluate the anti-tumor effects of these drugs on murine osteosarcoma cell lines, in terms of proliferation and apoptosis. We found that both YM175 and YM529 strongly inhibited the in vitro proliferation and induced apoptosis of murine osteosarcoma cells. YM529 was more effective than YM175 in inhibiting cell proliferation. These observations suggest that third-generation BPs directly affect on the proliferation and survival of osteosarcoma cells, which supports the possibility that they could be beneficial in the treatment of osteosarcoma patients.