Crude palm oil (CPO) can be processed into various types of derivative products such as cooking oil, margarine, ice cream, and soap. To obtain good quality CPO, physical and chemical purification methods are often applied. Ultrafiltration (UF) membranes are an alternative method to purify CPO. However, fouling is a major limitation in the application of UF membrane technology. The most common sources of fouling in the purification of CPO are phospholipids and fatty acids. In this research, fouling phenomena are investigated to understand the relevant fouling mechanism of UF membranes. This study aims to evaluate the performance of a UF membrane for separating isopropanol-oleic acid-lecithin feed solutions. UF performance is evaluated based on the flux and rejection of phospholipids and free fatty acid. The fouling was identified by the value of relative flux reduction, percent of fouling and the membrane morphology after filtration. This research confirms that addition of oleic acid results in a significant decline in flux. In addition, cake/gel layer blocking is established to be the blocking mechanism of the UF process.