The silver (0.5-3 at %) substituted nanosize hydroxyapatites (AgHAs) were synthesized by microwave processing. The X-ray diffraction (XRD) peaks are very broad, indicating that the AgHAs were of nanosize (30 nm). Transmission electron microscopy analysis shows needle-like morphology of AgHA, having length 60-70 nm and width 15-20 nm. The AgHA phase was stable up to 700°C without any secondary phases. The antibacterial effect of AgHA against Escherichia coli and Staphylococcus aureus was observed by spread plate method, even for low concentration of silver ions (0.5%) with 1 × 105 cells/ mL of respective bacterial culture, after a 48 h incubation period. However, some colonies of E. coli were seen with a high dose of 1 × 108 cells/mL after 24 h. The zone of inhibition by disc diffusion test method was found to vary with the amount of silver in the sintered AgHA pellets, for both the bacteria, after 24 h of inoculation. Osteoblast cell attachment in varying density was noticed on AgHA samples with 0.5, 1.0, and 1.5% silver substitution. However, osteoblast spreading was significantly greater on 0.5% AgHA compared to 1.0 or 1.5% substituted AgHA samples. Thus, the low amount of AgHA has a potential of minimizing the risk of bacterial contamination, without compromising the bioactivity, and is expected to display greater biological efficacy in terms of osseointegration. © 2006 Wiley Periodicals, Inc.