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The waste cooking oil (WCO) as a raw material for biodiesel production is recognized to be an attractive and economic alternative to the use of vegetable oils. However, the presence of high free fatty acids (FFA) and impurities of WCO may require several pretreatment before the transesterification. In this study, the FFA in WCO was esterified with methanol by a photocatalytic process under visible irradiation using Cu₂O, CuS and Ag₃PO₄ as the catalyst. Pretreated WCO was converted to biodiesel by basis catalyzed transesterification process. The optimum photocatalytic esterification was achieved using 10% catalyst with a methanol to oil ratio of 21:1, reaction temperature at 60^oC and irradiation from 200 W for 3 hours. During this process, the FFA were converted into fatty acid methyl esters. The results showed that all catalyst could be reducing FFA in WCO, which confirmed the % FFA conversion more than 55%.