Highly dispersed Pt-loaded ZSM-5 (Pt/ZSM-5) catalysts were prepared by a combination of ion-exchange and thermal pretreatment in different temperatures under vacuum. Highly dispersed ion-exchanged Pt2+ ions were reduced into Pt+ and then Pt-0, sustaining their high dispersion state with an increase in the thermal pretreatment temperatures up to 773 K. Thus, prepared Pt-0 highly dispersed in the cavities of ZSM-5 exhibited high catalytic activity for the oxidation of CO with N2O at 273 K. However, pretreatment at temperatures higher than 973K led to the aggregation of highly dispersed Pt-0 clusters, resulting in a decrease in the catalytic activity for low-temperature oxidation.