The degradation, by several advanced oxidation reactions, of a pulp mill ECF bleaching effluent, was studied. The initial biodegradability of the organic matter present in the effluent, estimated as the BOD 5 /COD, was low (0.3). When the effluent was submitted to ozonation and to five different advanced oxidation systems (O 3 /UV, O 3 /UV/ZnO, O 3 /UV/TiO 2 , O 2 /UV/ZnO, O 2 /UV/TiO 2 ), the biodegradability increase significantly. After five minutes of reaction, the O 3 /UV system appears as the most efficient in to transform the organic matter to more biodegradable forms. A similar effect was observed when the effluent was submitted to an activated sludge treatment. The COD, TOC and toxicity reduction correlated well with the biodegradability enhancement after AOPs treatments.