Purpose: This study was designed to examine the effects of a weight control program on body weight and the sense of efficacy for control of dietary behavior in psychiatric inpatients. Methods: A quasi-experimental design was used. Data were collected from March 1 to September 30, 2007. Female mentally ill patients in closing psychiatry ward of H University Hospital participated in the study (16 persons in the experimental group and 13 in the control group). Results: The weight control program including diet therapy, exercise, education and behavior modification therapy decreased the rate of weight gain in female mentally ill patients taking atypical anti psychotics, and effectively increased a sense of efficacy for control of dietary behavior. Conclusion: Weight control program had a positive effect as a nursing intervention to decrease obesity and to increase the sense of efficacy for control of dietary behavior of psychiatric inpatients in psychiatric inpatients.