Background:Children with early onset of callous unemotional ( CU traits are at risk for long term, persistent psychosocial problems The current study aimed to explore the characteristics of CU in preschool children with Attention Deficit Hyperactivity Disorder ( ADHD and the diagnostic significance of CU traits in ADHD. Method: A total of 227 preschool children (89 with ADHD, 51 with Autism Spectrum Disorder [ ASD ]], and 87 Typically Developing Children [ TDC ]]) aged 4 5 years old were recruited. The participants were diagnosed using the Diagnostic Infant and Preschool Assessment (DIPA), and assessed using t he Swanson, Nolan, and Pelham Rating Scale IV , The Inventory of Callous Unemotional Traits I CU ), t he Behavior Rating Scale of Executive Function Preschool Version BRIEF P )), and t he parent rated Strengths and Difficulties Questionnaire (SDQ ). Results: The results showed that there was a significant difference between ICU subscale scores and total scores among the ADHD, ASD and TDC groups F 59.87 P < 0.001 with the ASD group s coring the higheset 37.16±10.19 ) and the TDC scoring the lowest 20.39±7.40 )). T he callousness scores in the ADHD+ODD group showed the highest level of significance , and the ADHD only group was significantly higher than the TDC F 20.42 , P < 001) The ICU subscales showed low to moderate positive correlations with the SDQ subscales γ 0.21 ~ 0.68 P < 0.01) except the unemotional subscale T he ICU subscales were also negatively associated with the prosocial behaviour subscale γ = 0.45 ~ 0.68 P < The total ICU score was moderately and positively related to the BRIEF-P subscales (γ = 0.4 7 ~0.6 7 P < 0.01). The CU traits were also used to predict oppositional defiant symptoms β = 0.32, R2 = 0.11, P < 0.001). The callousness and uncaring subscale scores and the total ICU score were significantly correlated with ADHD symptoms and explained a significant 3 proportion of the variance (15-24%).Conclusions: The current study indicated that having high CU scores was associated with increased odds of having ADHD. Screening for CU traits could be used to predict ADHD diagnosis in preschool children .