Mono-dispersed SiO2-CaO bioactive glass nanospheres (BGNS) were prepared by a two step sol-gel method in the absence of surfactant. The size of BGNS ranged from 200 to 350 nm in diameter and exhibited a rough surface texture. In vitro biomineralization tests showed that BGNS could rapidly induce the deposition of an apatite layer in simulated body fluid (SBF). The effect of bioactive glass on the biomechanical properties of various mammalian cells was first reported in this paper. Atomic force microscopy (AFM) was used for measuring the biomechanical properties of mammalian cells. The result showed that BGNS-medium could significantly decrease the plasma membrane stiffness of bone marrow stem cells (BMSCs) by ∼50% and stimulate BMSCs spreading. The effect of BGNS on biomechanical properties of bovine aortic endothelial cells (BAECs) was opposite to that on BMSCs. BGNS increased the BAECs' stiffness and stimulated the elongation of endothelial cells and the formation of endothelial networks, which might potentially facilitate the vascularization of implanted BGNS-based biomaterials in tissue engineering as a scaffold or as an injectable system. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2010.