The recording of electroencephalogram from problem children began in 1938 with the work of Jasper, Solomon and Bradley1). D. Since that time, a number of reports has revealed the characteristics of the EEG in problem children. Recently attempts D 1) 2) 3) are made not only to understand properties of their EEG, but to relate them to the physiological or psychological factors of behavior disorder. But all of these researches are hardly satisfactory enough, because of lack of standardized trait of personality or lack of control of subjects. Therefore, in our present attempt purporting to establish the relationship between the EEG patterns in juvenile delinquents and their psychological personality, an effort was made especially to catch the psychological traits through more objective technique. Summary 1) The EEG on thirty delinquents from fourteen to fifteen years and twenty four school boys as control was examined. Through appearance of the theta waves and spikes, the delinquent EEG was significantly distinguishable from the control EEG. In delinquents the theta waves were observed more frequently on the frontal, central and temporal cortices, and spikes were more on the temporal and central cortices. 2) In order to investigate the relationship between EEG patterns and psychological traits, Rorschach test, Yatabe-Guilford test, Kraepelin and Intelligence test were used to the delinquents. The results lead: a) Decline of intelligence was discovered in the spike-group, b) According to the results of Rorschach and Y-G test, spike-group showed asocial and impulsive traits of anxiety, and theta-group was disposed of asociality and emotional immaturity, c) There was a significant relationship between EEG patterns and criminal classification of the delinquents.