Attention-deficit hyperactivity disorder (ADHD) is one of the most common psychiatric disorders in children. Poor academic readiness for school entry, fine motor skills, and social impairment are more common in preschoolers than healthy controls. Since dopaminergic system dysfunction is connected with numerous neuropsychological diseases, including ADHD, antipsychotic drugs are used for the treatment of ADHD. Considering the importance of ADHD treatment in preschoolers and the fact that psychostimulant drugs are less effective in preschoolers and have more adverse effects, this study is conducted to compare the safety and efficacy of risperidone and aripiprazole in the treatment of ADHD. Fifty-five 3-6-year-old children diagnosed with ADHD were randomized to a 12-week trial of treatment with risperidone or aripiprazole 1 . The assessment was performed by Parent ADHD-RS, Strengths and Difficulties Questionnaire (SDQ), Children's Global Assessment Scale (CGAS) before treatment, and weeks 2, 4, 6, and 12 of treatment. The study showed that the ADHD-RS score of both groups was significantly reduced after starting the treatment. After the 12th week, the score of aripiprazole's group was significantly less than the score of risperidone's group (pvalue = 0.019). In addition, the CGAS scores and the total SDQ score improved for both groups without any statistically significant difference between them. Both risperidone and aripiprazole are effective in the treatment of ADHD among preschool-aged children. Both drugs are welltolerated, significantly reduce the ADHD-RS score and the total SDQ score and improve the CGAS score.