[Purpose] The purpose of this study was to make a comparison of dynamic balance ability between dual and simple task conditions. [Subjects and Methods] Nine children with attention deficit hyperactivity disorder (9.00 ± 2.12 years) and 10 healthy children (9.67 ± 2.75 years) were recruited. Each group was asked to do an obstacle crossing alone and the obstacle crossing combined with a stimulus response task. The Qualisys motion capture system was used to capture full-body motion. The parameters measured included crossing speed, step width, and reaction time. [Results] Children with attention deficit hyperactivity disorder had greater problems than controls in performing the primary balance task while concurrently completing the auditory reaction time task and showed greater variability in step width and a longer reaction time. The balance scores assessed using the Movement Assessment Battery for Children test were significantly worse in the attention deficit hyperactivity disorder group and were significantly correlated to the crossing reaction time and variance of crossing speeds.[Conclusion] The attention deficit hyperactivity disorder group preferred to complete the obstacle crossings before responding to the stimulus. This resulted in a longer reaction time for the secondary task and also changed the gait strategy.