This study focuses on the ability to cooperate in solving diverse and complicated problems in our daily lives. It also aims to clarify the ability to cooperate, which is required for home economics education. At a fundamental level, this paper aims to make clear the dynamic process of developing national registered dietitians’ ability to cooperate and its influential factors in order to make suggestions with regard to home economics education. Many national registered dietitians have come from the faculty of home economics.They work in medical institutions that have called for the ability to cooperate, particularly through revision of the Nutritionists Law and revision of medical fees for nutrition therapy, and they work in cooperation with people like doctors, nurses, pharmacists, etc. Therefore this study focuses on the job classification of national registered dietitians in medical institutions.Data was obtained about cooperative activities through interviews with ten national registered dietitians with considerable work experience in medical institutions. The data was qualitatively analyzed by using the modified grounded theory approach.Below is a summary of my findings:(1) Twenty-five concepts and five categories classified according to conceptual meaning were createdfrom the data.(2) The process of developing national registered dietitians’ cooperation consists of two types of effort: inside and outside their place of work. Furthermore, these two types of effort were interrelatedand developed to improve development cooperation.(3) There are three factors that control the quality of cooperation：set- up cooperation , professional knowledge and skills, and the ability to manage synthetically.