Introduction: The rapid development of online games is currently marked by the increasing number of adolescent game players. This was particularly true during the COVID-19 pandemic that forced all activities to be done at home. Adolescents who play online games excessively, however, can risk their self-concept. Adolescents' ability to control the increasing habit of playing online games can help them reduce the risk of self-concept problems by enhancing their adaptive behavior at their crucial psychosocial development stage. Health education and group therapy can be employed to attain this goal. Aims: The authors of this study aim to determine the effectiveness of health education and group therapy regarding the self-concept of adolescents who play online games excessively. Methods: As the research design, this study applied a quasi-experimental pre-posttest with a control group. The research respondents were selected using the stratified, proportional, and simple random sampling techniques. Seventy-six adolescents comprised the respondents of this study, divided into two groups. The respondents' inclusion criteria were adolescents aged 15-16 years old who had played online games for at least the last 12 months. Results: The self-concept of adolescents in the intervention group has increased after implementing health education and group therapy (p < .05). In contrast to this, the self-concept of adolescents in the control group has not changed after implementing health education and group therapy (p > .05). Conclusions: Health education and group therapy effectively improve the self-concept of adolescent gamers.  Kulcsszavak: self-concept, adolescence, health education, group therapy, online games addictions