Objectives: Some studies reported a significant improvement in sleep parameters by melatonin therapy in children with ADHD. Utilizing risperidone along with stimulants is another pharmacologic approach for ADHD treatment. In this study we investigated the effect of melatonin and risperidone on sleep disorders in children with ADHD and compared their effectiveness as well.Methods & Methods: 29 patient aged 6 years to 12 years old with ADHD were randomly divided into two groups based on file number: either received melatonin (3 mg to 6 mg) combined with Ritalin or received risperidone (0.25mg to 0.5 mg) combined with Ritalin in a single blind randomized clinical trial. Assessments were performed at baseline and were repeated at 2 and 4 weeks after beginning of the treatment. Results:In risperidone group significant differences has been found in total score of sleep disorders (P=0.000), sleep onset and maintenance score (P=0.000), Sleep-wake transition disorders (P=0.000), but no significant differences in breathing (P=0.104), and hyperhidrosis (P=0.105) and excessive daytime sleepiness score (p=0.065), and in arousal group after 2 weeks (p=0.027) and after 4 weeks (p=0.150). comparison of melatonin group in different weeks (Base line with 2 and 4 weeks after treatment), show significant differences in total score of sleep disorders (P=0.000), sleep onset and maintenance score (P=0.000), Sleep-wake transition disorders (P=0.003), excessive daytime sleepiness (P=0.004), but no significant differences in breathing (P=0.068) and arousal (P=0.218) and hyperhydrosis score (P=0.336). Conclusion:The results showed the equal effect of risperidone and melatonin. It can be concluded that the risperidone has the same effect of melatonin in the treatment of sleep disorders in children with ADHD.