This pilot-scale study deals with highly polluting agro-industry's wastewater, palm oil mill effluent (POME). Ceramic ultrafiltration membrane was applied to treat this effluent. UF separation behavior of POME is reported. The effects of transmembrane pressure and crossflow velocity on permeate flux, limiting flux and percentage rejection for suspended solids and dissolved organic matters were investigated. The limiting flux obtained was further applied to determine critical flux and deposit resistance, R,, using the possible theoretical link of critical flux and limiting flux. The verified values of critical flux are useful in the operation of ultrafiltration to minimized membrane fouling; thus, longer lifespan of the membrane can be expected. Both transmembrane pressure and crossflow velocity show their significant effects to the permeate flux, whereas only the crossflow velocity influences the rejection of dissolved organic matters in terms of COD and BOD. (c) 2005 Elsevier Ltd. All rights reserved.