The presented study aimed to clarify the relationship between the autonomic nervous system and disruptive behaviors among preschoolers. Possible gender differences in autonomic activity were also examined. A total of 88 preschool-age children were enrolled in this study. Autonomic activities were measured by power spectrum analysis of heart rate variability (HRV). The Swanson, Nolan and Pelham parents and teachers rating scale (SNAP-IV) was applied to evaluate each subject's severity of disruptive behavior. The relationship between the HRV results and the SNAP-IV was evaluated by correlation analysis, which disclosed that the scores for inattention, hyperactivity/impulsivity and oppositional defiant disorder showed a negative association with LF % and LF/HF. The above scales, except for the hyperactivity subscale, also showed a positive association with HF. On separating the two genders, only boys showed the above correlations. Preschool-age boys who show more inattentive and hyperactive features have lower sympathetic and higher parasympathetic activity.