Purpose: This study was designed to investigate the effects of a network program to prevent obesity and improve dietary habits for patients taking antipsychotics or antidepressants. Method: Thirty-seven patients in two hospitals were assigned to a control group (21 patients) or an intervention group ( 16 patients). The intervention group was evaluated to analyze the effect of the network program for six weeks after the program. Result: There was a difference in the rate of increased body weight between the control group and the intervention group. Notably, the body weight of both groups before the intervention was significantly increased. However, after the intervention the body weight of the intervention group rarely increased, whereas, the body weight of the control group was significantly increased as expected. There was an observed difference in diet between the control group and the intervention group. After the intervention, caloric intake per day of the intervention group decreased. Also, the duration of the meal of the intervention group after the intervention was longer than before. Conclusion: The network program for preventing obesity and improving dietary habits of patients taking antipsychotics or antidepressants was effective. The study shows that a network program can be an important part of a nursing intervention in clinical practice.