Objective: This study examined the independent and interactive effects of acculturation and social activity on depressive symptoms. Method: Using a sample of community-dwelling Korean American older adults (N = 675), hierarchical regression models of depressive symptoms were estimated with an array of predictors: (a) demographic variables, (b) health-related variables, (c) acculturation, (d) social activity, and (e) an interaction between acculturation and social activity. Results: After controlling for the effects of demographic and health-related variables, both acculturation and social activity were identified as significant predictors. Moreover, their interaction was significant (β = .09, p < .05). Further analysis showed that the beneficial effect of social activity on mental health was particularly strong among those with lower levels of acculturation. Discussion: Our findings suggest that enhancing opportunities for social engagement may serve to protect and promote the mental health of vulnerable older immigrants, particularly those who are less acculturated.