It is one of the most important subjects in the industrial gear field to design gears fitted for reduction of material cost. The force-fitted gear is one of the promising gears which meets such a requirement. Some researches to elucidate the characteristics of force-fitted spur gears have been carried out for several years. However, the design method of force-fitted helical gears has not yet been established. Under such a present situation, taking up the research of a design method of force-fitted helical gears as the subject of the present paper, the allowable limits of rim thickness and interference were discussed from three points of view: stress at the root fillet of the gear tooth, dynamic slipping torque and stress in a tangential direction at the force-fitted surface of the gear rim. Consequently, the design procedure of the force-fitted helical gear was shown.