Due to the change in life style and diet, modern people suffer from obesity, diabetes, and other types of diseases. Regular practice of exercise can alleviate the negative effects from the diseases and even cure the diseases in certain cases. In addition, regular practice of exercise improves the quality of life. These facts have drawn much attention and people nowadays recognize the importance of exercise. As a result, more and more people hope to start exercising but they lack the knowledge of how and what to exercise. Professional counseling costs relatively expensive and thus it is difficult for ordinary people to access a counselor. To tackle these issues we propose a fuzzy expert system that designs a workout program. The system receives user's body information, preference on exercise style, and available time. Then, the system generates a customized workout program based on fuzzy reasoning. We conduct experiments to verify the performance of the proposed system. The participants enter their body condition, preference and available time and receive customized workout programs from the system. The experiments verifies the applicability of the system. The future research includes the extension of the system to meet various user demands and to reflect a number of expert knowledge sources.