Mesoporous bioactive glass microspheres (MBGMs) with large mesopores have attracted considerable attention in the field of bone tissue regeneration and drug delivery systems due to their excellent bioactivity, biocompatibility and high specific area. In this study, a loose structure of MBGMs with adjustable chemical compositions was synthesized by the combination of sol-gel and water-in-oil (W/O) microemulsion. All the prepared MBGMs possessed a large mesopore diameter that increased with CaO content, a high surface area and good apatite-inducing formation ability. In vitro protein absorption and release assays demonstrated that the MBGMs exhibited decreased loading efficiency and burst release behavior as the CaO content increased. Additionally, an enhanced BSA-loading amount and prolonged release curve were obtained after the surfaces of MBGMs were modified by amine groups. Furthermore, the preliminary in vitro cell experiments showed that MBGMs exhibited good biocompatibility. The results indicated that MBGMs could be a promising candidate as a drug/protein carrier for bone tissue regeneration. (C) 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.