Nonoxidative activation of methane was carried out over Ag/ZSM-5 catalysts, prepared by the wetness impregnation method, and the catalysts were characterized by various techniques. Theoretical calculation was further employed to clarify the reaction mechanism of methane coupling over the catalysts. Ag+ ions were found to be the main Ag species at low loading (1-5 wt %) whereas higher loading (10 wt %) resulted in metal Clusters. Combined with experimental evidence and computer modeling, it is concluded that isolated Ag+ ions play a crucial role in the catalytic coupling of methane under nonoxidative conditions.