Objectives : This study explored the differences in their ego defense mechanisms between adolescents with conduct disorder and normal adolescents. Methods : Subjects were 35 adolescents with conduct disorder and 44 normal adolescents. The Ewha Defense Mechanism Test (EDMT), consisting of 200 items and 20 scales, was administered, to examine the defense mechanisms of both groups of adolescents. Results : Normal adolescents presented statistically significantly higher scores on the reaction formation, controlling, suppression, anticipation, dissociation, and distortion scales than did adolescents with conduct disorder. Zn addition, adolescents with conduct disorder used neurotic defense mechanisms of both neurotic and mature levels less frequently than normal adolescents did. Factor analysis revealed that, normal adolescents had higher scores on ego-expansive factor scales and behavior control factor scales thanadolescents with conduct disorder did. Conclusion : The results suggest adolescents with conduct disorder use mature and ego-expansive defense mechanisms less frequently than do normal adolescents.