AbstractThe reactivity of nano silica (SiO2) with calcium hydroxide (Ca(OH)2) was evaluated and characterized in this study. Ca(OH)2 activated nano SiO2 takes place through an exothermic process, which is mainly attributed to the breakdown of SiOSi bonds. Ca2+ offsets the charge imbalance and bonds to SiOH and SiO− giving rise to calcium silicate hydrate (CSH) gel. Care has to be taken that the reactivity of nano SiO2 with Ca(OH)2 significantly depends on the Q3 percentage in nano SiO2. Q3 percentages significantly influence the reaction kinetic of nano SiO2. The higher Q3 percentage results in a higher reaction degree of nano SiO2 with Ca(OH)2 and shorter setting times of the pastes. The higher Q3 percentage results in a lower total reaction heat of nano SiO2 with Ca(OH)2. It is suggested that the Q3 percentages of nano SiO2 should be in excess of 30% to keep the satisfactory setting properties of the pastes for the application requirements of bone cement. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2011.