In this study, photo-oxidation process was thought to be a pretreatment step, where partial oxidation was effected before the biological treatment. The effects of this process on colour removal of the industrially fermented wastewater and its biodegradability were examined. Decoloration was investigated with UV, UV/H(2)O(2),, UV/TiO(2)/H(2)O(2), UV/ZnO/H(2)O(2) series and it was found that the highest colour removal efficiency is obtained with UV/H(2)O(2)/TiO(2) series, e.g. 60.98%. The improvement in biodegradability was determined by observing the BOD/COD ratio. In the UV/TiO(2) series, the optimization of irradiation time and catalyst amount were determined with respect to BOD/COD ratio. It was seen that the ratio increased from 0.11 to 0.18 at the end of the irradiation time of 120 min. TiO(2) amounts higher than 1 g L(-1) caused a decrease in the BOD/COD ratio. The improvement in treatment was supported by the oxidation rate constant (k) of organic matter, which was calculated via values obtained from BOD test. While the k value of untreated wastewater was 0.167 day(-1), it was calculated as 0.201 day(-1) for photocatalytically treated wastewater.