A principal object of the present invention is to provide a pharmaceutical composition that can produce a high antitumor effect by efficiently delivering a drug with antitumor activity to tumor tissues with the aid of carbonate apatite nanoparticles. The present invention provides a pharmaceutical composition including carbonate apatite nanoparticles with an average particle size of at most 50 nm containing a drug with antitumor activity and a pharmacologically acceptable solvent in which the carbonate apatite nanoparticles containing the drug are dispersed.
