Background and purposes: The CHEXI has been shown to be a cross-cultural, free-to-download, convenient and psychometrically proper tool to evaluate the exec-utive functioning (EF) of children in community. The present study evaluated the EF of children with autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), and comorbidity of ASD and ADHD as diagnosed by a pediatric psychiatrist by using the Taiwanese Traditional-Chinese CHEXI (TC-CHEXI) in or-der to explore how the tool can help us understand the EF in clinical samples. Methods: In total, the primary caregivers of 87 children participated; they com-prised 18 children with ASD (17 boys), 46 children with ADHD (34 boys), and 23 children with comorbid ASD and ADHD (22 boys). The Executive Functions Rating Scale for Children with ADHD was used to investigate the criterion-related validity of the TC-CHEXI. The correlations of the TC-CHEXI with the Behavioral Rating Scale for Children with Autism and the Repetitive Behaviors Scale-Revised were also explored. Group comparisons on their EF subcomponents were conducted with age, gender, and IQ controlled for. Results: The findings suggest that examining with the TC-CHEXI, the EF of the clinical samples comprised of ASD/ADHD were shown to be dysfunctional as expected. Furthermore, the TC-CHEXI was noted to have criteria-related construct validity in clinical settings. Conclusion: The results showed that the TC-CHEXI is a psychometrically reliable and valid EF assessment tool to be used in community settings for primary screening of ASD/ADHD.