Abstract: This work aims to analyze the contribution of H2O2 on ozonation of Sulfamethoxazole (SMX). A single ozonation was able to totally remove SMX. TOC and COD depletion rates after a transferred ozone dose of 60 mg/L was related to the formation and decomposition of H2O2. An increase on O3 gas inlet concentration from 10 g/m3 to 20 g/m3 improved COD abatement from 11% to 36%. When the presence of H2O2 at the beginning of ozonation was tested, it was verified that COD and TOC degradation were enhanced, attaining maximum values of 76% and 32%, respectively, when compared with 35% and 15% reached in a single ozonation Ver menos