Objectives: This study investigated the association between functional limitations and depressive symptoms among older adults in South Korea, focusing on gender differences in the moderating roles of relationship satisfaction with family, friends, and neighbors. Methods: Fixed-effect models were applied to five waves of data from the Korean Retirement and Income Study, encompassing 19,180 observations. Results: Increases in functional limitations were associated with higher levels of depressive symptoms, regardless of gender. However, the moderating effects of relationship satisfaction differed by gender: For older women, satisfaction with family moderated the association, whereas for older men, satisfaction with friends played a moderating role. Discussion: The findings suggest tailoring interventions to improve family relationships for women and friendships for men in mitigating depressive symptoms among functionally vulnerable older adults in Korea, where rapid population aging poses significant challenges to protect functional and mental health among older adults.