PURPOSE: To explore the relationship between social isolation and psychological well-being among community-dwelling older adults and analyze the mediating role of physical activity and psychological resilience in the chain mediation effect between social isolation and psychological well-being. METHOD: Two hundred sixty-five older adults from six communities in Baoding City were selected using convenience sampling. Social isolation, physical activity, psychological resilience, and psychological well-being were measured. The SPSS PROCESS program was used to test the chain mediation effect. RESULTS: Pearson correlation analysis indicated significant relationships between psychological well-being and social isolation, psychological resilience, and physical activity (all p < 0.001). Mediation analysis results showed that social isolation directly affects psychological well-being and influences psychological well-being through three mediation chains: physical activity, psychological resilience, and the chain mediation effect of physical activity and psychological resilience. Total mediation effect accounted for 60% of the total effect. CONCLUSION: Social isolation is a significant risk factor for decreased psychological well-being among older adults, and physical activity and psychological resilience serve as important explanatory mechanisms. Community health workers should prioritize the impact of social isolation on the psychological well-being of older adults and develop intervention strategies based on the pathways of physical activity and psychological resilience to enhance psychological well-being and promote healthy aging.