The Effect of Assertive Group Therapy on Assertive and Resilience Ability of Adolescent in Padangpanjang Junior High School. Adolescent's lack of ability in assertive behaviour causes deviant behaviour e.g. unable to express wishes, violate other people right and ask forcefully. One solution to overcome this is that assertive ability and resilience need to be improved through assertive group therapy. This study aims to find the effect of assertive group therapy on assertive ability and resilience of adolescents. Quasi Experimental Pre and Post-test with control group was used. Intervention has been performed to 42 participants while 42 others were as a control group. Six sessions of assertive group therapy has been done. The findings show that a significant increase of assertive ability in intervention group has been found (p= 0.000) while ability resilience also raises significantly (p= 0.015). On the other hand, no significant difference is noted between pre-test and post-test in control group since the value of assertive and resilience ability are (p= 0.287) and (p= 0.658) respectively. Moreover, a positive correlation (r= 0.0396) has been found between assertive ability and resilience ability. The therapy is recommended as one of health care treatment in society particularly for adolescent.