The purpose of the present study is, on the basis of Loevinger's theory, to examine whether delinquent adolescents show lower than the controls in the levels of ego development. One hundred female juvenile delinquents and 180 female high school students were administered the Japanese version of the Washington University Sentence Completion Test (WU-SCT). Their responses were rated according to Sasaki's manual (1981) in terms of the Loevinger's levels of ego development. It was found that the delinquents produced more responses of the lower levels than the controls, especially more responses on the Impulsive and Self-Protective levels. On the other hand, the delinquents produced less responses of the Self-Awareness level than the controls. These differences between the two groups were even observed in the analyses in which verbal ability, number of letters making incompleting sentence, and age were controlled. These findings suggests that adolescent delinquency was in some cases a result of a lower ego development.