The preparation of polyurethane (PU) foam using green-based polyol from soybean oil as an alternative for petroleum-based polyurethane. The polyurethane was fabricated by using the prepolymer method following the two steps namely epoxidation and alcoholysis reaction. The FTIR, hydroxyl numbers were used to monitor the process of the synthesized polyol and determined the physicochemical properties. Choosing a suitable method for the processing of polyurethane foam soy-based became a major to the success of the production. Temperatures of operation, reactants, were not the only ones to be considered, dealing with organics the length of the reaction should also be considered. The research aimed to focus on the optimized fabrication of soy-polyol as intermediate to flexible foam polyurethane. Identify the use of the length of reaction to epoxidation reaction, and hydroxylation, and evaluates the correlation to the physical property of the foam product.