OBJECTIVES: To assess the potential factors predicting the response in the treatment of attention-deficit/hyperactivity disorder (ADHD) children with atomoxetine in China Mainland, Taiwan, and South Korean. METHODS: A post-hoc analysis was done on a 24-week, prospective, open-label, multi-center, uncontrolled study of atomoxetine treatment. Participants were children aged 8 to 11 years, diagnosed with ADHD according to the Diagnostic and Statistical Manual of Mental Disorders, naiumlve to ADHD medications, and met the symptomatic severity threshold of 1.5 standard deviations above the age and gender norm for the ADHD-IV-Parent:Inv Rating Scale (ADHDRS) total score (ADHDRS-TS). Good treatment response was defined as age;40% improvement in ADHDRS-TS from baseline to week 24. Multiple logistic regression analysis with stepwise effect selection method was used to determine the factors (including baseline characteristics, ADHDRS-TS change at week 4) associated with treatment response at week 24. RESULTS: Among 228 children, the mean (±SD) age was 9.6 (±0.96) years and 85.1% were males. Thirty-six percent were from China Mainland, followed by Taiwan (33.3%) and South Korea (30.7%). The mean ADHDRS-TS at baseline was 35.3(±7.1) and 61.8% children had the combined ADHD subtype. Four (1.75%) children had historical illness. At week 4, the mean ADHDRS-TS decreased by 34.4 (±22.3) from baseline. By week 24, 73.7% children experienced good treatment response. The odds of being good treatment response at week 24 significantly increased by a factor of 1.69 (95% CI: 1.40 to 2.05, <0.0001) for each additional 10-points improvement in the ADHDRS-TS by week 4. The associations between treatment response and baseline characteristics were not detected. CONCLUSIONS: Most ADHD children exhibited good treatment response to atomoxetine. The participants with ADHDRS-TS improvement by week 4 were more likely to achieve good treatment response at week 24, which indicates that early response to atomoxetine might be considered as a predictor of the ultimate response.