Photo-catalytic activity of TiO2 and Au/TiO2 was studied in gas phase oxidation of ethylene (C2H4) in the presence of air over TiO2 and Au/TiO2 supported on glass surfaces using 350 nm photo-light separately. Around 20 nm-sized TiO2 synthesized by hydrothermal process and Au/TiO2 synthesized through photolysis of TiO2 (laboratory-prepared) with Au-III ions solutions were used for photo-catalytic oxidation experiments. CO2 was found as photolysis product and its yield was found to be increasing with the increase in C2H4 concentration up to 0.47 mM (with respect to irradiation vessel/apparatus) in TiO2 system, subsequently the CO2 yield decreased, which might be due to the decrease in O-2/C2H4 ratio. However, in Au/TiO2 (0.3-7.5 wt.% gold) system, the rate of photo-catalytic oxidation of C2H4 was reduced to half (0.05 ml min(-1)) as compared to pure TiO2 system (0.08 ml min(-1)). Besides this, studies on the photocatalytic oxidation of CH3OH and HCOOH in the presence of suspended TiO2 and Au/TiO2 in water were carried out separately to evaluate the extent of oxidation properties between two different phases' viz. gaseous and condensed phases. Our studies demonstrated the enhancement in photo-catalytic oxidation of CH3OH and HCOOH over Au/TiO2 in aqueous systems on contrary to the gas phase oxidation of C2H4. (C) 2010 Elsevier B.V. All rights reserved.