Removal of organic dyes from wastewater has become an important issue because of their carcinogenic and mutagenic effects. In this study, we prepared Ag-doped ZnO (Ag_ZnO) photocatalysts containing various amounts of Ag (0.05-0.5mol%) by a hydrothermal process followed by calcination at 500 °C and evaluated the photocatalytic degradation of methylene blue (MB) under sunlight irradiation. The incorporation of Ag into the ZnO lattice and the hexagonal wurtzite structure of the prepared catalysts could be confirmed by X-ray photoelectron spectroscopy and powder Xray diffraction analysis. BET analysis shows that the pore volume and pore size was increased with doping Ag into ZnO. The photocatalytic degradation of methylene blue followed a pseudo-first-order kinetics and the rate constant for dye degradation with 0.1% mol Ag was almost three-times bigger than that with bare ZnO. Our study shows that the photocatalytic activity of ZnO toward MB degradation under sunlight can be effectively enhanced by doping with Ag.