Prior research has shown that incremental beliefs about well-being can influence well-being in adults, but less is known about the relationship in adolescents and the potential underlying mechanisms that explain the relationship. The present study aimed at examining the association between incremental well-being beliefs and well-being in adolescents and the mediating role of self-esteem and optimism. Study 1 showed that incremental well-being beliefs predicted well-being in a sample of 390 adolescents aged 10–14, even after adjusting for age, gender, subjective family socioeconomic status, and incremental beliefs about ability and emotion. Study 2 used another sample (N = 405) to replicate this association and further found that self-esteem and optimism independently mediated the association. These findings provide initial evidence for the association between incremental well-being beliefs and well-being in adolescents and elucidate possible mediational mechanisms (i.e., self-esteem and optimism) of how incremental beliefs about well-being are linked to well-being.