Colloidal Ca 1 0 (PO 4 ) 6 (OH) 2 (HA) particles doped with Cr 3 + ions in different mole ratios (Cr/(Ca- + Cr) = X C r ) by a coprecipitation method were characterized by ICP, XRD, N 2 adsorption, TEM, EPMA, TG, XPS and FTIR. Ca 2 + ions of HA were substituted by Cr 3 + ions in one to one at X C r 0.13. The particle size increased with an increase in X C r . When doped at X C r 0.13 irregular particles were formed besides long rectangular particles containing Cr 3 + ions less than ca 0.03 in X C r . The compositions of these two kinds of particles showed that the long rectangular particles were HA and the irregular particles were hydrated calcium chromium phosphate hydroxide. The growth of HA crystals was strongly promoted by doping Cr 3 + ions.