Controllable drug delivery is one of the important ways for the therapy of bone cancer. Conventional mesoporous silica nano-particles may lack dual properties for combining controllable delivery of anti-cancer drugs and bone-forming bioactivity for bone cancer therapy. The aim of this study is to synthesize mesoporous bioactive glass (MBG) nanospheres with combined dual functions of bioactivity and controlled drug delivery, and to further investigate their delivery property of anti-cancer drugs as well as the functional effect on bone-cancer cells. MBG nanospheres with spherical morphology and internal mesoporous microstructures were successfully prepared by a facile hydrothermal method. The prepared MBG nanospheres possess high specific surface area and mesopore volume (443 m2 g−1, 0.57 cm3 g−1) as well as uniform mesopore size distribution (2.9 nm). The MBG nanospheres demonstrate excellent bioactivity by inducing apatite mineralization in simulated body fluids. An anti-cancer drug, doxorubicin hydrochloride (DOX), was successfully loaded in the MBG nanospheres with a distinctively high loading efficiency of around 90%. The loading amount of DOX can be effectively controlled by adjusting the initial drug-loading concentrations. MBG nanospheres can maintain a sustained release of DOX, and their release kinetics can be controlled by varying the pH microenvironment and initial drug-loading concentrations. In addition, the prepared MBG nanospheres showed obvious degradation by releasing Ca2+ and SiO44− ions in PBS. Furthermore, the delivery of DOX from MBG nanospheres into cell culture environment shows a significant inhibitory effect on the viability of osteosarcoma cells with the increase of interaction time. The prepared MBG nanospheres have high specific surface area and mesopore volume, excellent apatite-mineralization ability, distinct degradability, high DOX-loading efficiency and controllable DOX release as well as anti-cancer functions. These unique characteristics suggest that the obtained MBG nanospheres may be used for the therapy of bone cancer.