Membrane Bioreactor (MBR) is effectively improve effluent quality through membrane separation and increasing concentration of activated sludge. Although the MBR process is broadly used in water treatment and reclamation, membrane fouling is a critical problem in both industries and academics, especially in application of industrial wastewater. Due to the complex composition and high fluctuation of influent water quality, the MBR used in industrial wastewater generally suffering more difficult operation and maintenance problem. This study dealing with MBR used in petrochemical wastewater, one of the typical industrial examples in Taiwan, and aiming to figure out the main fouling types. With long-term monitoring and regularly samples analysis, we can understand the causes of fouling and optimizing the cleaning strategies as a reference for practical operators.