Purpose: Meager research has been carried out to determine the effectiveness of the token economy among patients behaving violently in mental hospitals. The purpose of this study was to examine the effectiveness of the Short-Term Token Economy (STTE) on violent behavior among chronic psychiatric in-patients. Methods: A nonequivalent control group design method was utilized. Participants in an experimental group (n=22) and control group (n=22) took part in this study from January to April, 2008. Observation on aggressive behavior among male in-patients in one hospital as a baseline was made during the week before the behavior modification program and measurement of aggressive behavior was done using the Overt Aggression Scale (OAS), which includes verbal attacks, property damage and physical attacks. Results: The aggressive behavior scores of the experimental group decreased, those of the control group, scores showed an increase after the eight-week behavior modification program utilizing STTE. Conclusion: The results of the study indicate that STTE is effective in reducing the incidence of aggressive behavior among male in-patients in psychiatric hospitals. The outcome of this study should be helpful in reducing the use of coercive measures or psychoactive medication in controlling the violent behavior among in-patients in hospitals.