The aim of this study was to examine the effects of cognitive behavior group therapy (CBGT) and family psychoeducation (FPE) in promoting and maintaining adolescent mental health. This quantitative study used a quasi-experiment method, pre- and post-testing with a control group design. A total of 86 adolescents were selected using the purposive sampling method and allocated into two groups that were administered different types of intervention. The first intervention group was provided with mental health education and adolescent developmental stimulation only, which was carried out with individual exercises of stimulation. The second intervention group was provided with mental health education and adolescent developmental stimulation in addition to CBGT and FPE. A mental health continuum short-form questionnaire was used to determine mental health scores. The results showed that most of the adolescents received flourishing mental health scores. These scores significantly increased after receiving mental health education and developmental stimulation, as well as CBGT and FPE. Our results indicate that mental health education and developmental stimulation can be used to promote and maintain good mental health. CBGT and FPE can be used not only to treat mental health problems but also to promote flourishing mental health.