The purpose of this study was to explore the mental aspects(心法的 側面) of a tennis learner based on self-study. Using the self-study methods, data were collected from the reflective diaries of the researcher who had written about the learning experiences of tennis for 8 years. The data were analyzed by the constant comparative method. The meanings and contexts of the mental aspects of a tennis learner were categorized into three themes. First, in ‘kindness causes positive emotions’, the creation of pleasure through consideration and praise were examined. Second, in ‘unkindness causes negative emotions’, such unkindness as contempt raising dissatisfaction, reproving causing anger, and overacting creating uncomfortable moods were described. Third, in ‘anxiety causes performance mistakes and reveals my weaknesses', negative effects of anxiety were unveiled.