Introduction: One of the most commonly diagnosed psychiatric disorders in children is attention deficit hyperactivity disorder (ADHD) which according to diagnostic criteria, it includes high symptoms, attention deficit disorder and impulsivity.Objective: The aim of this study was to determine the relationship between serum vitamin D levels in children with attention deficit hyperactivity disorder (ADHD) and healthy children.Method: This case-control study was conducted in a sample of 70 patients, including 35 cases and 35 controls in the range of 4 to 12 years old. Data was analyzed by SPSS-20 statistical software and descriptive statistics (absolute and relative frequency, mean and standard deviation), and qualitative analytical objectives of Chi-square and Fisher test and for comparison of mean serum in two groups, T-test was used.Results: The results of the study showed that 64.3% of the children in the study group were female and 35.7% were boys. The mean age of the patients with ADHD was 7.971 ± 1.56 and in the control group was 6.486 ± 1.4years.The results showed that the mean level of vitamin D in children with attention deficit hyperactivity disorder (98.8 ± 26.514), while the mean in healthy children (36361±63636) which there was statistically significant (P ≥ 0.001) between two groups. The average level of vitamin D in ADHD subtypes and ADHD severity was different, but there was no significant (p≤0.05) difference between the mean serum levels in patients with severity and type of hyperactivity.Conclusion: The results of this study showed that the level of vitamin D in children with attention deficit hyperactivity disorder is especially mild and severe, with a lower average, and also a low level of vitamin D intake. So, considering maternal nutrition during pregnancy and lactation, child nutrition, parent awareness and the use of vitamin D supplements may be effective in reducing the risk of hyperactivity disorder in children.