In a previous work it was reported adapted Trametes versicolor FPRL 28A INI culture was used to treat undiluted olive mill wastewater (OMW) without addition of any nutrients with significant amount of total phenolics were removed. However, decolorization was not so pronounced. Therefore, the aim of this study is to enhance the efficiency of dephenolization and decolorization of the primary treatment with adapted Trametes versicolor, incorporating a secondary biological treatment step using different microorganisms with sequential batch and co-culture applications. Through sequential batch applications Funalia trogii ATCC 20080 was found to have a higher potential in terms of total phenolics removal and decolorization amongst the tested organisms and better results were obtained from sequential batch applications as compared to co-culture experiments. In sequential batch applications, up to 91% total phenolics were removed and 64% decolorization was achieved after 24 days with 20% (v/v) inoculation rate of F. trogii when malt extract broth was used in inoculum preparation. In addition, significant accumulation of laccase (2019 +/- A 121.13Ul(-1)) and manganese peroxidase (463 +/- A 33.89 Ul(-1)) activities were attained. In co-culture applications highest total phenolics removal and decolorization were 78 and 39%, respectively, with non-adapted T. versicolor, whereas highest laccase and manganese peroxidase acitivities were obtained with F. trogii as 2219 Ul(-1) +/- A 176.14(.) and 513 +/- A 4.12 Ul(-1), respectively.