Bioceramic composites were synthesized by sintering the powders of hydroxyapatite (HAp) mixed directly with additive of 0.5, 1.0, 2.0, 5.0 and 10 wt.%SiO2, respectively, at 1200℃. X-ray diffraction (XRD) analysis indicated that the phase transformation from HAp to tricalcium phosphate (TCP) comprising α-TCP and Si-TCP occurred and became more prominent with the addition of SiO2 and the increase in SiO2 content. The observations of their surface microstructures showed that the addition of SiO2 suppressed the grain growth and promoted the formation of crystallineglassy composites denoted HAp + TCP/Bioglass. As the SiO2 content is as high as 5 wt.%, the composite made a feature of crystalline clusters with different sizes consisting of HAp and TCP grains surrounded by the matrix of glassy phase. Furthermore, the dependence of in vitro bioactivity of these composites on the SiO2 content was biomimetically assessed by determining the changes in surface morphology, i.e., bone-like apatite layer growth, after soaking in an acellular stimulated body fluid (SBF) for 3 days at 36.5℃. It was found that the HAp-SiO2 composites showed a much faster bone-like layer growth than pure HAp, and the propensity of composites to exhibit a better bioactivity was getting more notable with increasing SiO2 content, except for the case of the highest content of 10 wt.%. It was believed that the formation of the bone-like layer on the surfaces of these biocomposites is closely related to the increasingly provided silanol groups and transformed TCP phase in materials associated with the content of SiO2 added.