The purpose of this study is to explore whether training psychological capital is effective on mental health and subjective well-being in adolescence. A quasi-experimental design was used with pre-test and post-test data evaluations, comparing an experimental group with a control group. In this study, the statistical population included adolescent girls with problematic mental health (age 13–15) referred to an Arian psychological clinic from April to June 2021 in Borujerd, Iran. The study included twenty-three adolescents selected through a purposive sampling method and randomly divided into two groups, experimental (n=12) and control (n=11). To collect data, mental health and subjective well-being questionnaires were administered. For the experimental group, Psychological capital intervention was administered in ten sessions of 90 minutes every two weeks while the control group received no treatment. MANOVA in SPSS software version 23 was used for data analysis. Results suggest that the Psychological Capital intervention had positive effects on mental health (P <0.001, F = 18.88) and subjective well-being (P<0.001, F= 16.36) in adolescent girls with problematic mental health. This study reveals that PsyCap intervention is effective at improving mental health and subjective well-being. This study provides encouraging new evidence for the efficacy of psychological capital (PsyCap).
