Objective: This study executed to evaluate the effectiveness of Music-Harmonic Movement therapy on aggressive behaviors in children with moderate to severe intellectual disability (ID). Method: In this semi-experimental Participants recruited from a daily care-training rehabilitation center under supervision of Qom's Welfare Organization in 2009. Forty children with moderate to severe ID were selected, and randomly assigned in two experimental and control groups. Aggressive behaviors recorded based on a researcher-made checklist. Beethoven's third symphony and harmonic movement protocol administered three times per week on participants. Findings: Data analysis by ANCOVA showed that Music-Harmonic Movement Therapy could decrease aggressive behaviors. Conclusion: Music-Harmonic Movement Therapy can be useful for aggression treatment in children with ID.