Objective This study examined the association between the wave form in quantitative electroencephalography (QEEG) and the cognitive and behavioral characteristics measured by the Korean version of Wechsler Intelligence Scale for Children 4th edition (K-WISC-IV), Korean version of the attention deficit/hyperactivity disorder Rating Scale (K-ARS), and Korean version of Child Behavior Checklist (K-CBCL) in children diagnosed with ADHD. Method A retrospective cross-sectional study was performed on children aged 8 to 13 years, who were diagnosed with ADHD at Samsung Medical Center from November 2011 to March 2017. A total of 57 ADHD children were selected by a medical chart review. Their QEEG findings and psychological test results, including K-WISC-IV, K-CBCL, and K-ARS (n=42), were collected. The QEEG was analyzed by the ranges of Hz: delta (1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), and beta (12–25 Hz) and transformed to the z-scored relative power. The collected data were analyzed using Pearson and Partial correlation analysis. Results The Letter-Number Sequencing scores of K-WISC was positively correlated with fronto- central alpha. The hyperactivity/impulsivity scores of K-ARS were positively correlated with the theta/beta ratio. Among the items of K-CBCL, social immaturity was positively correlated with delta and theta, and negatively correlated with alpha. Social competence was negatively correlated delta and theta, and positively correlated with alpha. Conclusion These results suggest that the resting state QEEG results of children with ADHD may reflect their cognitive and behavioral characteristics, especially in working memory/executive function, hyperactivity/impulsivity, and sociality.