The bioactive glass of composition 53SiO(2)-6Na(2)O-22CaO-11K(2)O-5MgO-2P(2)O(5)-1B(2)O(3) (1-98)has been prepared using the melt method. The ultrasonic velocities, attenuation and elastic properties measurements have been made operated at a fundamental frequency of 5 MHz at room temperature on bioactive glass 1-98 before and after different thermal treatment conditions. Further, the frequency dependence of the attenuation was fitted into a linear relation alpha = af(N). The observed linear increase in velocities, density and elastic properties of bioactive glass as a function of thermal treatment temperature, indicates that the densification in bioactive glass is due to the change in network bond per unit volume and not due to the structural/cross-linkage changes. Thus, thermal treatments of bioactive glasses lead to changes in elastic properties of bioactive glass. Furthermore, a long-term thermal treatment at higher temperatures also seemed to cause such changes to the glass surface that the formation of Ca,P-layer was inhibited during a 48 h immersion in simulated body fluid (SBF). (c) 2005 Elsevier B.V. All rights reserved.