In vitro dissolution and antibacterial activity of Ag nanoparticle-containing hydroxyapatite (HA) powders (AgNPHAP) synthesized by precipitation method were evaluated in this study. AgNPHAP were immersed in Tris-HCl solution with 30 mM Cl ions to estimate the in vitro dissolution behavior. The amount of Ag ions in Tris-HCl solution first increased and then decreased because Ag ions reacted with Cl ions to form AgCl. The antibacterial activity of AgNPHAP increased with increasing amounts of AgNPs attached to the HA powders in both 1/500 nutrient broth (NB) and undiluted NB solutions, which had Cl ion concentrations of 0.2 and 100 mM, respectively. These results indicate that HA powders as Ag nanoparticle carriers can effectively prevent bacterial infections despite AgCl precipitation, even under simulated biological conditions such as in undiluted NB solution.