This study examined the relationship between economic well-being and mental health in young adults and investigated the mediating effects of young adults’ self-esteem. This study used the National Longitudinal Survey of Youth 79 for Children and Young Adults. 9,584 young adults were selected, and the mediation model was conducted. Results showed that economic well-being is related to self-esteem and depression during adulthood. Self-esteem is significantly associated with mental health among young adults. Results show evidence of partial mediation of the relationship between economic well-being and mental health by young adults’ self-esteem. Economic well-being is one of the most important factors to develop and cultivate self-esteem and reduce mental health problems during young adulthood. Economic well-being is critical for developing self-esteem during young adulthood, and this study reveals that developing higher self-esteem is important for one’s mental health during young adulthood. Self-esteem should be considered to better understand mental health during young adulthood in the context of individuals’ economic well-being.