Ag/ZnO nanocomposites have been successfully prepared via a facile microwave method without any post-synthesis treatment. This is a facile and rapid process requiring only low power of microwave irradiation (120 W). The formation mechanism of Ag/ZnO nanocomposites was clearly discussed. The photocatalytic performance of the Ag/ZnO nanocomposites with different Ag contents for degradation of methylene blue was systematically evaluated. The Ag/ZnO nanocomposites showed enhanced photocatalytic activities compared with pure ZnO. Specifically, the photocatalytic activities of Ag/ZnO nanocomposites increased with increasing Ag content from 0.5 to 1.5 %. However, further increasing Ag content to 2.0 % induced the formation of more agglomerates, which could act as recombination centers of photoexcited electron-hole pairs, leading to decreased photocatalytic activity. It is believed that this facile, rapid microwave-assisted strategy is scalable and can be applied to synthesize other noble metal/semiconductor oxide nanocomposites for different applications.