Background: There is still concern about delayed mental development for children born through Intra-Cytoplasmic Sperm Injection (ICSI). In the present study, the intelligence quotient (IQ) of ICSI children at the age of 5–6 years was compared with that of the control group of naturally born (NB) children. Outcome measure: Full-scale IQ of the mental development in children born through ICSI in 5–6 years. Design: Cross-sectional study. Setting: Fatemehzahra Infertility and Reproductive Health Research Center of Babol – Iran. Participants: 28 live-birth singleton children 5–6 years of the first generation born after ICSI treatment. Methods: The mental development of 28 born through ICSI children at 5–6 years compared with 32 naturally born children as control using intelligence quotient (IQ) test obtained from the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) (Iranian version). Results: The mean full-scale IQ was 105.9 ± 14 for ICSI and 107.2 ± 12.9 for NB children which showed no significant difference. The only significant possible predictors of slightly lower full-scale IQ in ICSI children were lower parental education level and longer childcare in day center. Conclusion: Our finding provides some reassurance for parents of children born through ICSI regarding the child’s preschool IQ.