In the present study, Fenton and sono-Fenton processes were applied to the oxidative decolorisation of synthetic textile wastewater including CI Reactive Orange127 and polyvinyl alcohol. Process optimisation [pH, ferrous ion (Fe2+) and hydrogen peroxide (H2O2)], kinetic studies and their comparison were carried out for both of the processes. The sono-Fenton process was performed by indirect sonication in an ultrasonic water bath, which was operated at a fixed 35-kHz frequency and 80W power. The optimum conditions were determined as [Fe2+]=20mgl-1, [H2O2]=15mgl-1 and pH=3 for the Fenton process and [Fe2+]=25mgl-1, [H2O2]=5mgl-1 and pH=3 for the sono-Fenton process. The colour removals were 89.9% and 91.8% by the Fenton and sono-Fenton processes, respectively. The highest decolorisation was achieved by the sono-Fenton process because of the production of some oxidising agents as a result of sonication. Consequently, ultrasonic irradiation in the sono-Fenton process slightly increased the colour removal to 91.8%, while decreasing the hydrogen peroxide dosage to one-third of that of the Fenton process. © 2011 The Authors. Coloration Technology © 2011 Society of Dyers and Colourists.