Objective. To explore the relationship between body constitution (BC) types and weight change in patients with schizophrenia and who underwent second-generation antipsychotics (SGAs) treatment. Method. Body weight and waist circumference of eighty-five participants were measured for 6 consecutive weeks. Constitutions of Yin-Xu, Yang-Xu, and Stasis were assessed using the Body Constitution Questionnaire (BCQ). Results. Participants with body constitutions Yin-Xu (50.6%), Yang-Xu (49.4%), or Stasis (38.8%) exhibited worse physical condition and unhealthy daily habits, particularly in Stasis constitution. Moreover, Stasis constitution was significantly associated with several factors, including BMI, body weight, waist circumference, perception of stress, perception of health, staying up late, and less physical exercise. However, perception of stress showed significant difference in Yin-Xu, Yang-Xu, and Stasis. Generalized estimating equation (GEE) analysis revealed that significant time effects in body weight increase in the imbalanced BC types and gentleness BC type. SGAs induced weight gain in imbalanced BC type as well as gentleness BC type, especially treated with olanzapine. Conclusions. This is the first study to explore the longitudinal relationship between BC and weight gain in schizophrenia patients undergoing SGAs treatment. Health care providers should focus on weight gain problems in schizophrenia patients who underwent SGAs treatment.