BACKGROUND: Laccases are receiving increasing attention as potential industrial enzymes in various applications. Therefore, it is important to find inexpensive and optimized media for large-scale commercial production. The present work aims to valorize olive mill wastewater (OMW) by its use as base media for laccases production by Trametes trogii and use of the laccases produced for decolorizing textile dyes. RESULTS: A high yield of 25 120 U L-1 of laccases was obtained at an OMW: water ratio of 80:20 enriched with 2 g L-1 of urea corresponding to initial biochemical oxygen demand (BODs), chemical oxygen demand (COD) and total phenol concentrations of 18.4, 46 and 4.6 g L-1 respectively. The partially purified laccases resulted in 85% decolorization of blue tubantin GLL 300 and black tubantin VSF 600, and 45% decolorization of blue solophenyl after 6 h of incubation. Subsequent additions of the same dye dose to the reaction mixture resulted in a very significant decrease in laccases activity after the third dye addition. CONCLUSION: The use of OMW for laccases production is a cost effective process. The laccases produced can be applied to the decolorization of textile wastewaters. (C) 2009 Society of Chemical Industry