An application of optimization design process for reduction of Thomas force of rocket turbopump turbines is presented in this paper. Because of its special specification, rocket turbopump turbine blades have higher loading. In such a situation, there is a possibility of rotor vibration problem generated by turbine instability force, that is, “Thomas Force”. Actually in the past engine development in Japan, there was the shaft vibration problem due to “Thomas Force”. In order to reduce shaft vibrations, it is important to keep “Thomas Force” small. In this paper, the results of optimization for the existing rocket turbopump turbine by using Robust Design Process and Multi-Objective Genetic Algorithm(MOGA)are discussed.