Ozonation of distillery slop waste was done to evaluate the process in terms of organic matter removal and decolorization efficiencies. The chemical properties of melanoidins, which are known to harbor the chromophoric groups in the waste were also investigated. Ozone had primary effects on the decolorization of the slops and improvement in its biodegradability, compared to organic matter removal (as COD). A decolorization efficiency of 80% and a biodegradability improvement of 40% was obtained in 40 hours. Only 16% of the COD was removed. The melanoidins had a 10% decrease in molecular weight indicating slight depolymerization. UV spectral studies of melanoidins showed that olefinic linkages (which are said to be important in the structure of the chromophores) decreased.