Objective To explore the effect of fluoxetine on the brain function of bulimia nervosa (BN) patients.Methods Seven female BN patients,who met criteria of the 3rd version Chinese Criteria of Mental Diseases (CCMD-3),accepted functional magnetic resonance imaging (fMRI) examinations before and after the antidepressant treatment (fluoxetine (20 mg/day)) for three months.Seven normal controls accepted the same fMRI examination only at baseline.fMRI imaging was block-design.Blocks of food or non-food stimulus containing pictures selected from International Affective Picture System (IAPS) which were shown by computer automatically.All subjects were evaluated by Hamilton anxiety scale (HAMA),Hamilton depression scale (HAMD17) and Likert Scale-likelihood evaluation to the same pictures in the fMRI imaging blocks.Results The average intensity and volume activated in BN before treatment were both significantly lower than that in the control (P＜0.05).But under stimulus of food pictures,bilateral prefrontal cortex and left amygdala of BN patients were significantly activated.After fluoxetine treatment,the intensity and volume activated both increased significantly (P＜0.01) and the main areas being activated were right temporal,cerebellum and bilateral prefrontal cortex.Conclusion Fluoxetine improves the bulimic symptoms of BN patients and decreases abnormal activation of prefrontal and limbic in these areas.The underline mechanism may be related to functions of serotonin system in prefrontal-limbic path.