Abstract: In this study, Ag/γ-Al₂O₃ catalysts were synthesized by an Ar dielectric barrier discharge plasma using silver nitrate as the Ag source and γ-alumina (γ-Al₂O₃) as the support. It is revealed that plasma can reduce silver ions to generate crystalline silver nanoparticles (AgNPs) of good dispersion and uniformity on the alumina surface, leading to the formation of Ag/γ-Al₂O₃ catalysts in a green manner without traditional chemical reductants. Ag/γ-Al₂O₃ exhibited good catalytic activity and stability in CO oxidation reactions, and the activity increased with increase in the Ag content. For catalysts with more than 2 wt% Ag, 100% CO conversion can be achieved at 300 °C. The catalytic activity of the Ag/γ-Al₂O₃ catalysts is also closely related to the size of the γ-alumina, where Ag/nano-γ-Al₂O₃ catalysts demonstrate better performance than Ag/micro-γ-Al₂O₃ catalysts with the same Ag content. In addition, the catalytic properties of plasma-generated Ag/nano-γ-Al₂O₃ (Ag/γ-Al₂O₃-P) catalysts were compared with those of Ag/nano-γ-Al₂O₃ catalysts prepared by the traditional calcination approach (Ag/γ-Al₂O₃-C), with the plasma-generated samples demonstrating better overall performance. This simple, rapid and green plasma process is considered to be applicable for the synthesis of diverse noble metal-based catalysts.