Responses of mesenchymal stem cells (MSCs) cultured with zinc-added (2 and 5%) bioactive glass granules were evaluated in terms of cell growth and osteogenic differentiation. MSCs were cultured with different quantities (3, 10 and 30) of glass granules for up to 21 days in the osteogenic medium. Cell growth was stimulated by a small quantity of glasses, particularly those that contained zinc. Osteogenic differentiation, as assessed by alkaline phosphatase activity (ALP) activity, was significantly enhanced by the glasses, particularly with large quantities of glass and for prolonged culturing. Expression of bone-sialo protein (BSP) was significantly up-regulated around the bioactive glass granules. Moreover, the zinc addition significantly altered the ALP and BSP depending on the culture time and glass quantity. Cellular mineralization was improved in all glass samples, and particularly in the 2% zinc-glass. Taken together, the zinc addition to bioactive glass induced the MSCs growth and their osteogenic differentiation, at least to the level of zinc-free glass, and with even higher level observed depending on the quantity and culture time. These findings indicate that the zinc addition to bioactive glass may be useful in development of biomaterials for the stimulation of adult stem cell in bone tissue engineering.