The purpose of this thesis was to analyze the phenomena of adapting to the process of in-service tennis training by elementary school teachers. To achieve the purpose of this study, the researcher used Ground Theory of Qualitative Analysis and 2-teachers of high-level group, 2-teachers of middle-level group and 2-teachers of low-level group of whole learners were chosen by purposeful sampling. The methods of getting various data for this study were observing participation, training journals, in-depth interview and questionnaires. The results of this thesis can be summarized as follows. First, teachers who participated in tennis training recognized the important roles of tennis. Second, teachers participated with the purpose of developing their skills, making good use of their spare time and promotion of their health. Third, the prime phenomena of the occurrence of adapting to the process of in-service tennis training by teachers were increased intention to play tennis, higher passion for tennis, the endeavor to develop skills, technical and mental difficulties. Fourth, the prime phenomena were placed in affirmative and negative situations. Fifth, teachers who participated in tennis training used strategies of reciprocal actions which were negative and positive. Finally, this study showed us a tendency of continuous enjoyment of tennis and recognition of the importance of health on adapting to the process of these in-service tennis training. ※ Key Words : in-service tennis training, prime phenomena.