Composites (CaP-DENPtNPs) of calcium phosphate particles (CaPs) with Pt nanoparticles protected by dendrimers (DENPtNPs) were synthesized at different pH following a hydrothermal synthesis method. The CaP matrix in CaP-DENPtNPs composites possessed hydroxyapatite crystalline structures at pH 12 and 8, but monetite crystals were obtained at pH 4. The particle sizes of the composites increased with decreasing pH, and at the same time the amount of PtNPs in the composites also increased. Furthermore, it was confirmed that CaP-DENPtNPs were mesoporous nanocomposites, and DENPtNPs nanoparticles were incorporated mainly on the surface of CaP particles at high pH, but most of DENPtNPs were encapsulated inside CaPs at low pH. The uptake of well-dispersed Pt nanoparticles up to 60 wt% in CaPs suggests the possibility of these materials as effective catalysts. Copyright 2014 Elsevier Inc. All rights reserved.