The purpose of this study was to determine the perceived psychological benefits and explore the mechanisms underlying the link between exercise and psychological well-being for a group of older adults (65-72 years; 6 women; 4 men) who participated in a 12-week program of moderate-to-high intensity resistance training. They were interviewed in-depth at 1 week preintervention, 1 month after commencement, and 1 week after completion. The participants believed that resistance training enhanced their well-being, and they gave various physical, mental, and social reasons to explain this link. In particular, self-efficacy and social interaction were found to be key mechanisms underlying this relationship. This study exposed meaningful perceived improvements in psychological well-being that have not been uncovered in quantitative studies of healthy older people undertaking resistance training. The findings highlight the importance of using qualitative methods to enrich understandings of the positive effect of exercise on psychological well-being. The findings also have implications for designing effective resistance training interventions for older people.