Biologically pretreated dyehouse effluent was further treated using enhanced ozonation in the presence of granular activated carbon (GAC). The effect of GAC addition to the ozonation process on color, chemical oxygen demand (COD), and total organic carbon (TOC) abatement has been studied. Decolorization kinetics were not influenced by GAC addition, whereas COD and TOC removal rates and efficiencies were significantly improved in the presence of GAC at pH less than or equal to7. Control experiments conducted in the absence of ozone (O-3) showed that GAC served as an oxidation catalyst in the heterogeneous treatment system rather than as an adsorbent. Moreover, GAC could be used in at least six sequential batches without replacement or regeneration of the catalyst medium.