Structure of hydroxyapatite (HAP) is more flexible towards ionic substitutions. Properties such as solubility, antimicrobial property can be tailored by substitutions. Substituted hydroxyapatite and fluorapatite of formulae BiNaCa3(PO4)(3)OH, Bi0.5M0.5Ca4(PO4)(3)OH (M = K, Ag), Ca10-xCux(PO4)(6)(OH/F)(2) d (x=0.05-025) and Bi0.5Na0.5Ca4(PO4)(3)F were synthesized and characterized by powder XRD, FT-IR, SEM-EDAX and TGA. In vitro solubility of the synthesized compounds was studied in the phosphate buffered medium of pH 7.4 at 37 degrees C. Based on the release of calcium and phosphorus ion concentration and pH, the solubility of these compounds is discussed. Bismuth and sodium co-substituted hydroxyapatite are found to be more soluble compared with other substituted apatite compounds and unsubstitutecl hydroxyapatite. (C) 2015 Elsevier B.V. All rights reserved.