Attention-deficit/hyperactivity disorder (ADHD) is an important challenge in studies of children's ethology that unbalances the opposite behaviors for creating inattention along with or without hyperactivity. Nevertheless, most studies on the ADHD children, which employed the EEG signals for analyzing the ADHD influence on the brain activities, consid- ered the EEG signals as a random or chaotic process without considering the role of these opposites in the brain activities. In this study, we considered the EEG signals as a biotic process according to these opposites and examined the ADHD effect on the brain activity by defining the dual sets of transitions between states in the complement plots of quantized EEG segments. The results of this study generally indicated that the complement plots of quantized EEG signal have a surprising regularity similar to the Mandala patterns compared to the chaotic processes. These results also indicated that the probability of occurrence of dual sets in the complement plots of ADHD children was averagely different (p < 0.01) from that of healthy children, so that the SVM classifier developed by these probabilities could significantly separate the ADHD from healthy children (99.37% and 98.25% for training and testing sets, respectively). Therefore, the complement plots of quantized EEG signals rele-vant to the ADHD children not only can quantify informational opposition caused from inattention, hyperactivity and impulsivity, but also these plots can provide remarkable information for developing new diagnostic and therapeutic techniques.<br />In this study, we examined 40 children with age range 7–10 years, in which 20 children were with ADHD (50% are healthy). These children were distinguished by helping a professional psychiatrist and information gathered from the detailed history of past and current<br />functioning, and also the Conner's parent rating scales [34]. Fig. 1 shows T scores of impulsivehyperactive extracted from the Conner's parent rating scale for all of the children. As seen in this figure, the T scores of impulsive-hyperactive for healthy children were approximately lower than 50, while these scores for the ADHD children were higher than 50. For each ofthe children, the EEG signals were recorded from the Fz, Cz, Pz, C3 and C4 positions on the scalp according to 10– 20 international system and under eyes-open resting conditions at 250 s. Average of A1 and A2 electrodes was employed as reference value.<br /><br />Asst. lac. Mohammed T. Fakhri