Objectives:The purpose of this study was to verify discriminant validity and the clinical cutoff score of Child Behavior Checklist 1.5-5 in the diagnosis of developmental delayed infants. Methods:The participants were screened by Denver II which includes 156 developmental delayed infants and 288 normal infants. Chi-squared test, t-test, ROC curve analysis, odds ratio analysis were performed on the data. Results:Only 47 items out of 99 items among the CBCL 1.5-5 of total groups, 36 items of boys and 48 items of girls, discriminated developmental delayed infants well. Discriminant validity was confirmed by mean differences on the subscales of Withdrawn, Sleep Problems, Attention Problems, Internalizing Problems, Externalizing Problems, Total Problems, DSM Pervasive Developmental Problems and DSM Attention Deficit/Hyperactivity Problems between the two groups. Additionally, ROC analyses demonstrated that Withdrawn, Attention Problems, Internalizing Problems, Total Behavior Problems and DSM Pervasive Developmental Problems significantly predicted developmental delayed infants compared to normal infants. Also, the clinical cutoff score criteria adopted in the Korean CBCL 1.5-5 for subscales of Withdrawn, Attention Problems, Internalizing Problems, Total Behavior Problems and DSM Pervasive Developmental Problems were shown to be valid. Conclusion:The subscales of Withdrawn, Attention Problems, Internalising Problems, Total Behavior Problems and DSM Pervasive Developmental Problems significantly discriminated in the diagnosis of developmental delayed infants well.