Mesostructured Pt/TiO2 nanocomposites have been synthesized at different Pt (0–2 wt%) and anatase/rutile ratios through simple one-step sol–gel reactions. The as-made mesostructured hybrids were subjected to H2 gas for 2 h at 450 °C to obtain ordered hexagonal mesoporous Pt/TiO2 nanocomposites with highly crystalline TiO2. Subsequently, the samples were calcined at 350 °C in air for 4 h to remove the surfactant. XRD data clearly show that biphasial anatase and rutile mixtures are formed by the addition of the Pt islands. The TEM results indicated that TiO2 and Pt, are partly in close contact; the lattice fringes exhibit the typical distances, i.e., Pt (111) (2.2 Å) and TiO2 (101) (3.54 Å). TiO2 nanoparticles with an average diameter of about 10 nm particles are not agglomerated and quite uniform in size and shape. Also, Pt nanoparticles are well dispersed and exhibit diameters of about 5–12 nm based on the Pt content. Our photocatalysts have been compared with colloidal 0.5 wt% Pt loaded onto commercial photocatalysts either UV-100 Hombikat or Aeroxide TiO2 P25 by the determination of the initial rate of HCHO formation generated by the photooxidation of CH3OH in aqueous suspensions to calculate the corresponding photonic efficiencies. The overall photocatalytic activities of 0.5 wt% Pt/TiO2 nanocomposites are significantly 3-times higher than that of colloidal 0.5 wt% Pt loaded onto commercial photocatalysts either UV-100 Hombikat or Aeroxide TiO2 P25. To the best of our knowledge, the measured photonic efficiency ξ = 15.5% of hexagonal mesostructured Pt/TiO2 nanocomposites is found to be among the highest ξ values reported up to now. The superiority of Pt/TiO2 is attributed to the bicrystalline (anatase/rutile) framework, large surface area, high crystallinity and mesoporous structure of Pt/TiO2 nanocomposites.