Mesoporous anatase TiO 2 was prepared for photocatalysis from TiOSO 4 solution. The samples were undoped or doped with chromium. The diffuse reflectance spectra of the samples and the morphology of the TiO 2 particles exhibited strong dependency on the preparation conditions. The mesoporous samples showed good photoactivity upon degradation of acetaldehyde in the visible range (>400 nm) and on degradation of methylene blue in aqueous solution in the UV range (366 nm). The catalyst activity demonstrated strong dependency on crystal size, on particle morphology and porosity, and on doping. Samples heated at 473 K were the most active in the gaseous phase and samples heated at 673 K in the aqueous phase. The pore size of the samples increased upon heating. The chromium-doped samples maintained activity at longer wavelengths (>420 nm) than the undoped samples.