The purpose of this study was to examine the relationships between an instructor’s professionalism determined by Pilates participants, participants’ physical self-description, and their subjective happiness. Due to the rapid growth of Pilates, we aimed to provide basic data on Pilates instructors’ program management and understanding of members’ needs by verifying the factors that make participants feel happy and sustained through Pilates. The study involved women participating in Pilates in Seoul and Gyeonggi Province from June to August 2019. Correlation analysis was used before regression analysis to predict the correlation between variables, and a multiple regression analysis was used to identify the effect of relationships and significant factors between each variable. Finally, in order to verify the effect of the mediator variable in the process of the independent variable affecting the dependent variable, a three-step mediator analysis process of Baron and Kenny (1986) was conducted. As a result of the regression analysis, the teaching technique, a sub-factor of the instructor’s professionalism, influenced the physical self-description of participants. Physical attractiveness, physical activity, sport competence, sub-factors of physical self-description as a mediator affected on Subjective happiness. Only teaching technique, a sub-factor of instructor’s professionalism, showed a statistically significant effect on subjective happiness. Next, as a result of identifying the mediating effect of the physical self-description, it was verified that the physical attractiveness and sport competence of the physical self-description had a partial mediating effect on the relationship between the instructor’s professionalism and subjective happiness.