The objective of this study is to investigate membrane fouling caused by ultrafiltration (UF) when reusing tertiary effluent in an industrial park. A bench-scale membrane system was performed. Experimental results showed that the removal of iron, manganese, and turbidity were 62%, 30%, and 77%, respectively. From the infrared ray analysis of membrane fouling, one can see that the organic functional groups were aromatic rings and a few linear chain compounds of chromophore and auxochrome found in dyestuff. Therefore, tertiary effluent may induce both colloidal and organic fouling into the UF system. (c) 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.