A continuous process was designed and optimized at conceptual stage for biodiesel production from waste vegetable oils. Unlike previous studies, the process was optimized taking into account the technical and economic considerations, simultaneously, to find the optimum operating conditions in the commercial scale productions. The effect of major design variables on the process yield was studied by modeling of esterification and transesterification reactors. Free fatty acids’ (FFAs) mole fraction in feedstock, production rate, conversion and molar ratio of the reactants in both reactors were chosen as major design variables. By considering the economic potential as objective function of process optimization, the optimum FFA mole fraction was obtained as about 0.50 (24 wt %). Also, the optimum values of conversion and molar ratio of the reactants in the esterification and transesterification reactors were found as 82-89% (depending on the different production rates), 11:1 and 96%, 8:1, respectively. It was found that economic potential increases linearly as production rate increases. Therefore, the production rate should be set at its maximum possible practical value. The break-even point at the optimum values of these variables, as mentioned above, occurs at the production rate of 157 ton/yr.