Decolourisation and decomposition of acid orange 7 as a model for textile wastewater was performed under subcritical water conditions in the presence of hydrogen peroxide. Hydrogen peroxide showed very efficient activity for decolourisation of AO7. Complete decolourisation temperature of AO7 declined from 275 to 135 degrees C when a sufficient amount of hydrogen peroxide was used in the reaction medium. The effects of several other parameters were also investigated. Reaction time as well as the initial amount of hydrogen peroxide showed great effect on the decolourisation and decomposition reactions. At the higher temperatures, it was found utilising UV/Vis scanning spectra that the dye decomposed into very small molecules and gaseous products; consequently, total organic carbon (TOC) amount of the solutions after subcritical water treatment significantly declined. The reactions carried out without formation of any solid materials. At the optimum conditions treatment of several different types of dyes were also investigated.