Mesoporous TiO2 film photocatalysts supported on stainless steel substrates were prepared using the sol-gel method with Ti(OC4H9)(4) as a precursor and poly ethylene glycol (PEG) as a structure-directing agent. Mesoporous TiO2 film with a pore diameter of about 15 nm was obtained with the addition of PEG (molecular weight =400). The pore diameter of TiO(2)film was varied with molecular weight of PEG additive. The structure-directing process was also discussed. Mesoscopically ordered inorganic/polymer composites were believed to form during the process. Compared to conventional TiO2 film photocatalyst, the mesoporous TiO2 film showed a good performance for the photo degradation of rhodamine B (RB) solution irradiated with UV light of 365 nm. The photo degradation constant of rhodamine B for mesoporous TiO2 film photocatalyst can arrive at 22 times of that for conventional TiO2 film photocatalyst. Also an excellent performance for the degradation of gaseous formaldehyde with mesoporous film photocatalyst was obtained. The photo degradation rate of gaseous formaldehyde for mesoporous TiO2 film photocatalyst can arrive at six times of that for conventional TiO2 film photocatalyst.