A significant enhancement in the catalytic activity of Au/TiO2 in CO oxidation and preferential oxidation reaction by creating the active sites on the catalyst surface by thermal treatment as well as by producing small gold particles by plasma treatment has been studied. Au/TiO2 catalyst (Au (1 wt%) supported on TiO2) was prepared by conventional deposition-precipitation method with NaOH (DP NaOH) followed by washing, drying and calcination in air at 400 degrees C for 4 h. Thermal treatment of Au/TiO2 was carried out at 550 C under 0.05 mTorr. A small amount of Au/TiO2 catalyst was taken from the untreated and thermally treated Au/TiO2 and both kinds of catalysts were treated with plasma sputtering at room temperature. The activity of the catalysts has been examined in the reaction of CO oxidation and preferential oxidation (PROX) at 25-250 degrees C. Thermally treated Au/TiO2 showed better catalytic activity as compared to the untreated catalyst. There is also an additional enhancement in the catalytic activity due to plasma sputtering on the both kinds of catalysts. Thermally treated Au/TiO2 followed by plasma sputtering Au/TiO2 showed higher conversion rates for CO oxidation reaction compared with untreated, thermally treated and plasma sputtered Au/TiO2 catalysts. It may be concluded that the enhancement of catalytic activity of thermally treated Au/TiO2 followed by plasma sputtering is owing to the generation of active sites such as oxygen vacancies/defects in TiO2 support using thermal treatment as well as by producing small gold particles using plasma treatment.