Treatment of olive mill wastewaters (OMW) by membrane techniques were investigated in this study. For this purpose. OMW was centrifuged, and filtered via UC010 ultrafiltration membrane followed by filtration through NP010, NP030, and NF270 nanofiltration membranes, and XLE and BW30 reverse osmosis membranes. Besides, skipping the ultrafiltration step, the centrifuged OMW was filtered through NP010 and NP030 membranes in order to evaluate the performance of the centrifuging process as a pretreatment option. For the OMW percolated through ultrafiltration membranes, the membrane fluxes reached values of up to 21.2, 5.2, 28.3, 15.5, and 12.6 L m(-2)h(-1) for NP010, NP030, NF270, XLE, and BW30 membranes, respectively. The maximum COD removal efficiencies obtained at 10 bars were 60.1%. 59.4% and 79.2% for NP010, NP030, and NF270 nanofiltration membranes, respectively, while they were 96.3% and 96.2% for XLE and BW30 reverse osmosis membranes, respectively. Besides, conductivity removal efficiencies obtained at 25 bars were 93.2% and 94.8% for XLE and BW30 membranes. respectively. Obtained efficiencies are higher than those obtained in the treatment of OMWs with other treatment methods. Thus, it was concluded that membrane processes are a good alternative for the treatment of OMWs. Additionally, the centrifuging process was found to be a promising pretreatment method. (C) 2010 Elsevier B.V. All rights reserved.