In this study, the oxidative decolorization of C.I. reactive yellow 145 (RY 145) from synthetic textile wastewater including RY 145 and polyvinyl alcohol by Fenton and sono-Fenton processes which are the combination of Fenton process with ultrasound has been carried out. The effects of some operating parameters which are the initial pH of the solution, the initial concentration of Fe2+, H2O2, and the dye, temperature, and agitation speed on the color and chemical oxygen demand (COD) removals have been investigated. The optimum conditions have been found as [Fe2+]=20mg/L, [H2O2]=20mg/L, pH 3 for Fenton process and [Fe2+]=20mg/L, [H2O2]=15mg/L, pH 3 for sono-Fenton process by indirectly sonication at 35kHz ultrasonic frequency and 80W ultrasonic power. The color and COD removal efficiencies have been obtained as 91 and 47% by Fenton process, and 95 and 51% by sono-Fenton processes, respectively. Kinetic studies have been performed for the decolorization of RY 145 under optimum conditions at room temperature. It has been determined that the decolorization has occurred rapidly by sono-Fenton process, compared to Fenton process. Color and chemical oxygen demand removals from synthetic textile wastewater including RY 145 and polyvinyl alcohol by Fenton and sono-Fenton processes were examined. The results show that decolorization was affected by following parameters: the initial concentration of the dye, Fe2+, H2O2, the initial pH, temperature of reaction solution, and agitation speed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.