Titanium-doped hydroxyapatite (Ti-HAp, (Ca10-2x, Ti-x, square(x)) (PO4)(6)(OH)(2), square: defect in Ca site) powders were modified with a CaMoO4 aqueous solution. Then their photocatalytic activity under UV illumination was evaluated by the decomposition of gaseous 2-propanol. The crystal structure, morphology, light absorption, and specific surface area were almost unchanged by the modification, but small clusters were deposited onto the Ti-HAp surface. The photocatalytic activity of the Mo-modified samples increased concomitantly with increasing Mo concentration until 0.5% against Ti. The highest photocatalytic activity of Mo-modified Ti-HAp was about nine times higher than that of Ti-HAp. Computer modeling revealed that the contribution of MoO42- doping into the Ti-HAp structure plays no important role in the activity increase. A Mo(V) signal appeared by UV illumination in electron spin resonance spectra of Mo-modified Ti-HAp. The Mo modification decreased the photoluminescence intensity. These results suggest that photoinduced electrons can transfer from the Ti-hybridized band to the cluster, thereby improving the carrier separation efficiency and engendering higher photocatalytic activity.