The aim of the study was to investigate the relation between self-identity and health-related quality of life (HRQOL) in adolescence. This study assumed that four aspects (i.e. personal, social, ability, and academic identity) of identity firmness could predict adolescent's HRQOL more than four aspects of identity importance. Meanwhile, this study also hypothesized that psychological and social relationships domains of HRQOL could be largely explained by the concept of identity firmness. One hundred and ninety-eight female adolescents participated in this study. Each participant completed a booklet containing the measures of the Questionnaire of revised edition of identity importance (QII-R), the Questionnaire of revised edition of identity firmness (QIF-R), the WHOQOL-BREF Taiwan version, and Visual-analogue HRQOL items. This study administered multiple regression analyses to test our hypotheses. The results demonstrated the concept of identity firmness could predict adolescent's HRQOL more than the concept of identity importance. The results also supported our hypotheses that psychological and social relationships domains of HRQOL could be largely explained by the concept of identity firmness. In general, this study supported our hypotheses that the concept of identity firmness is a crucial predictor to adolescent's HRQOL.