Gold nanoparticle is the active catalyst for CO oxidation at low temperature. This feature of gold base catalysts is suitable to overcome the problem of cold-start problem of automobile exhaust TWC converters. In this study gold nanoparticle were deposited on modified NH₄-Y type zeolite. The activity of synthesized catalyst was measured in a fixed-bed quartz-tubular reactor (7mm i.d.) under atmospheric pressure. In order to investigate the catalytic activities toward CO oxidation reaction, 31mL/min of air and 0.155mL/min of carbon monoxide were mixed and then passed through the reactor. It was found that activity of Au/Y catalyst was 100% at 20 ° C. The thermal stability of Au/Y catalyst was measured at 400 ° C for 4h. The activity of the catalyst was decreased to 65% at 20 ° C after thermal stability test. Results of Energy Dispersive Analysis by X-rays before and after thermal stability have showed that Au content of these samples were 3.89% and 1.76, respectively. It was found that the amount of Au content decreased after thermal stability process. Fourier Transform Infrared (FT-IR) spectra showed no changes in framework structure of zeolite during thermal stabilization process of the catalyst.