The purpose of this study was to examine which aspects of coresident intergenerational relationships were associated with the life satisfaction of unmarried children in established adulthood and of their parents. In this study, the coresident relationship characteristics included support exchange, emotion, interference-conflict, and perceptions of coresidence. Data were collected from (a) 250 never-married adults who were 35+ years old and lived in Seoul with at least one parent aged 75 years or younger and (b) 250 older adults who were 75 years old or younger and had at least one unmarried child aged 35+ years living in the same household. Our multiple regression analysis of unmarried children showed that the adult child’s financial support, the adult child’s psychological reliance on parents, the parent’s psychological reliance on the child, and relationship quality were significantly related to higher levels of life satisfaction. In contrast, the parent’s daily interference, daily conflicts, and anticipation of future care of parents were related to lower levels of life satisfaction. Second, the characteristics that were positively associated with the parent’s life satisfaction were the parent’s instrumental support, relationship quality, the coresident child’s daily interference, positive perceptions of intergenerational coresidence, and expectation of future care of parents. In contrast, the parent’s financial support, daily conflicts with the child, and taking intergenerational coresidence for granted were negatively related to the parent’s life satisfaction. This study advances our understanding of coresidence between unmarried children in established adulthood and their older parents by focusing on the multiple aspects of intergenerational coresidence.