Various energy-saving technologies have been developed because improved fuel consumption contributes. Pre-swirl fins, which consist of multiple fins installed in front of a propeller, swirl inflow to the propeller in the opposite direction of the propeller rotation to recover the waste energy of a propelled ship. The propeller mast be designed in consideration of pre-swirl inflow, because velocity distributions flowing into the propeller are changed by pre-swirl fin. This paper describes a propeller optimization method in consideration of pre-swirl inflow using real-coded genetic algorithm. A propeller was designed by utilizing the present method. Propeller tests in which influence of pre-swirl inflow of the original and improved propellers were carried out.