OBJECTIVE: This study aimed to explore the effect of cognitive function, social activity participation and social support on quality of life (QoL) of community-dwelling elderly. METHODS: The data on 194 elderly were selected from the nationwide community cohort named Korean Longitudinal Study on Cognitive Aging and Dementia. All subjects were assessed QoL-Alzheimer's Disease (QoL-AD), Cumulative Illness Rating Scale, exercise habit, Mini-Mental State Examination, social activities, The Medical Outcomes Study-Social Support Survey. The data were analyzed with SPSS WIN V. 21.0 program. RESULTS: The mean of QoL among community-dwelling elderly was 35.49 (24–46) for QoL measured by QoL-AD. The variables of professional, residence status, physical health, exercise, cognitive function, social activity participation and social support explained 29.3% of variance in QoL of community-dwelling elderly. Among these factors, the significant predictors of QoL were social support (β=0.322, p<0.001), cognitive function (β=0.152, p=0.021), and religion activity (β=0.152, p=0.025). CONCLUSION: The study suggests that the focus of intervention program should be on cognitive function and social activity participation to improve QoL for elderly. Improving cognitive function and social activity will lead to the network of social support, consequently to increase QoL for elderly living in the community.