Water scarcity in Mediterranean areas such as Comunidad Valenciana (Spain) makes water reuse necessary in high water-consuming industries. Previous studies by our research group showed that nanofiltration (NF) membrane permeates could be reused in some processes of finishing, dyeing and printing in the textile industry. In this work, biologically treated textile wastewaters were subjected to ozonation as a pre-treatment stage to NF. The aim was to reduce organic matter in order to prevent membranes from fouling and to oxidize organic wastewater compounds that could damage the membrane material. NF experiments were carried out in a laboratory plant equipped with a pressure vessel containing one spiral-wound membrane element (2.51 m(2) of active surface). With ozonation, wastewater COD was reduced up to three different levels (160, 135 and 82 mg/L). NF experiments with wastewaters of different organic matter concentrations were carried out studying the effect of increasing the feed concentration periodically. Conductivity retentions higher than 65% were achieved, with no significant flux decay observed during the experiments.