Dispersive Ag nanoparticles were formed on the surface of crystalline ZnO particles, using a photochemical reduction technique, to produce the Ag/ZnO with high photocatalytic performance. The prepared Ag/ZnO particles, as well as the ZnO particles without Ag attachments, were characterized using x-ray diffractometer, transmission electron microscope, and surface area analyzer. The abilities of the ZnO and the Ag/ZnO particles to photocatalytically decompose methylene blue under 365-nm ultraviolet light irradiation were evaluated by determining the corresponding specific reaction rate constant, k '(MB,m) (based on the mass of the photocatalyst used). While the ZnO crystalline particles (k '(MB,m)>0.43m(3)/(kg min)) already possessed better photocatalytic performance than the commercial photocatalyst P25 (k '(MB,m)=0.39m(3)/(kg min)), the Ag/ZnO particles exhibited much better photocatalytic performance than the ZnO particles. The highest k '(MB,m) for the Ag/ZnO particles was 1.93m(3)/(kg min), which was about five times that of the P25.