Gold nano particles (GNP) were deposited on Na-Y and H-Y zeolite substrates using chloroauric acid (HAuCl4) solution. The synthesized catalysts were then characterized and the catalytic activity toward CO oxidation reaction was investigated using a tubular fix bed micro reactor under atmospheric pressure. It was found that CO conversion of 100% and 5% can be achieved at 20 A degrees C on Au/Na-Y and Au/H-Y fresh catalysts, respectively. Thermal stability of catalysts was also investigated by treating the catalysts at 400 A degrees C for 4 h. After thermal stability test, activity tests of the catalysts at 20 A degrees C were shown that CO conversion of Au/Na-Y catalyst was decreased to 65% whereas the activity of the Au/H-Y at 20 A degrees C was increased up to 15%. Characterization tests were revealed that the structures of the zeolitic supports were remained unchanged after thermal pretreatment.