Platinum nanoparticles (PtNPs) protected by dendrimer were incorporated in calcium phosphate particles, and the degradation of a pollutant, formaldehyde (HCHO), in water was investigated by means of the resultant composite powders as a catalyst. The reaction was performed with dissolved oxygen from air as an oxidant. The analytical results elucidated that high PtNP and HCHO concentrations and high temperature effectively accelerated the oxidation of HCHO. The results were also kinetically analyzed using the Elovich equation. Additionally, the complete oxidation process of HCHO could be concluded to depend on the adsorption process of HCHO on the catalyst. Eventually, the present system is a valuable catalyst usable under the atmospheric oxygen at atmosphere pressure and at mild temperature, and more importantly this is a catalytic system easy removable from the reaction solution.