Transient reaction of adsorbed monolayer of acetic acid was used to compare the photocatalytic properties of TiO2 (Degussa P-25), titanium silicalite (TS-1) and Ti-MCM-41. TS-1 and Ti-MCM-41 catalysts with Si/Ti ratio of 50 were prepared by in-situ crystallization. The catalysts were characterized using XRD and UV-DRS. During photocatalytic oxidation (PCO), CO2 and HCHO were formed on P-25 TiO2, whereas CO2 and CH4 formed on TS-1 and Ti-MCM-41. Acetic acid decomposed photocatalytically on P-25 TiO2 to form CO2, CH4 and C2H6. On the contrary, CO2 and CH4 were formed on TS-1 and Ti-MCM-41 during photocatalytic decomposition (PCD). The rates of product formation during PCD were lower than PCO. The TS-1 and Ti- MCM-41 catalysts were less active per gram of catalyst. However, the TS-1 and Ti-MCM-41 catalysts had much higher adsorption capacities for organics. Therefore, it seems that the TS-1 and Ti-MCM-41 catalysts have some advantages in applications to PCO of organic comtaminants under conditions where the organic concentrations vary widely.