A novel mesoporous bioactive glass (MBG) of composition 64SiO 2 –26CaO–10P 2 O 5 (mol %) was prepared by hydrothermal method using H 3 PO 4 as a precursor for P 2 O 5 . The effect of use of organic triethylphosphate (TEP) and inorganic H 3 PO 4 in MBG synthesis on glass transition temperature (T g ), crystallinity, morphology and bioactivity of MBGs was studied. Phase purity determination and structural analysis were done using powder X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, respectively. XRD revealed that MBG prepared from H 3 PO 4 (MBG-H 3 PO 4 ) when sintered at 700 °C was partially glassy/amorphous in nature and contained a mixture of crystalline apatite, wollastonite, calcium phosphate and calcium silicate phases. Calcined MBG prepared from TEP (MBG-TEP) contained only wollastonite and calcium silicate phases. Particle size and surface area determined by BET surface area analysis showed higher surface area (310 m 2  g −1 ) for MBG-H 3 PO 4 as compared to MBG-TEP (86 m 2  g −1 ). It also had a smaller particle size (20 nm) and 70 % higher pore volume (0.88 cm 3  g −1 ) for MBG-H 3 PO 4 as compared to MBG-TEP (60 nm particle size and 0.23 cm 3  g −1 pore volume). Thermal studies showed that use of H 3 PO 4 decreases T g and increased ΔT (difference between T g and crystallization initiation temperature Tc o ). Low T g and high ΔT also enhanced bioactivity of MBGs. Bioactivity was determined by immersion in a simulated body fluid for varying time intervals for a maximum period of 14 days. It revealed enhanced bioactivity, as evident by the formation of apatite layer on the surface, for MBG-H 3 PO 4 as compared to MBG-TEP. Scanning electron microscopy and FTIR spectroscopy also supported this observation. Antibacterial studies with Escherichia Coli bacteria, MBG-H 3 PO 4 showed better antibacterial behaviour than MBG-TEP. © 2014, Springer Science+Business Media New York.