This study aimed to obtain basic information to develop an Acceptance and Commitment Therapy (ACT) program for ADHD children and adolescents. Exploratory studies of two themes were conducted. First, we performed both Korean version of the Avoidance and Fusion Questionnaire for Youth (K-AFQ-Y) and Korean Child and Adolescent Mindfulness Measure (K-CAMM) in an ADHD group and a normal control group, and verified the significant difference between the two groups. The ADHD group had significantly greater psychological rigidity than the normal control group, suggesting the need for ACT for ADHD children and adolescents. Second, we identified the correlation between the T scores of standardized neuropsychological tests and the total scores on the K-AFQ-Y and K-CAMM, in the ADHD group. Some correlative tendencies were identified, although the statistical significance was not sufficiently verified due to the small number of participants used in the analysis. Therefore, we discussed the implications of these results. This study is also meaningful because it is the first to examine the relationship between the construct of ACT and the executive dysfunction of ADHD children and adolescents.