A novel metal-semiconductor nanocomposite with stable metal nanoparticles and efficient photocatalytic performance has been prepared. It consists of highly dispersed ∼2 nm platinum (Pt) nanoparticles loaded on mesoporous and bicrystalline TiO2 fibers (Pt/mb-TiO2). Due to the well organized porous Pt/TiO2 nanoarchitecture, rate of photodegradation of CHCl3 was nearly doubled compared to both P25 and Pt/P25. And in photocatalytic production of H2 (with methanol as an electron donor), Pt/mb-TiO2 presented much more stable activity than Pt/P25. In a 20 h H2 production, Pt nanoparticles on P25 agglomerated and grew remarkably from 2.0 ± 0.5 nm to 4.5 ± 2.5 nm, while Pt nanoparticles on mb-TiO2 changed slightly from 2.0 ± 0.5 nm to 2.2 ± 0.5 nm. Moreover, the loss ratio of Pt on P25 is 36%, which is much larger than that of 7% on mb-TiO2. The efficient charge transfer in the interfaces of Pt/TiO2(B) and TiO2(B)/anatase was discussed. We concluded that the high photocatalytic performance of Pt/mb-TiO2 can be attributed to stable Pt nanoparticles supported on the mesoporous masonry frameworks of TiO2 and efficient charge transfer in the interfaces.