Purpose: This study was to determine the mediator or moderator role of social support in the relationship between stress and depression among family caregivers of older adults with dementia. Method: Sixty nine family caregivers were randomly selected from health care centers in P city and a face-to-face interview was conducted using questionnaires from January to May of 2002. Data were analyzed with descriptive statistics, Pearson correlation, and hierarchical multiple regression using SPSS program. Result: Family caregivers of older adults with higher dependency in ADLs and higher problematic behaviors, provided care to the older adults for a longer period of time, and perceived less social support reported higher depression. Social support showed mediating effects between stress and depression, while did not show moderating effects. Elderly dependency on ADLs and caregiving duration decreased perceived social support and decreased social support increased depression. Conclusion: To increase family and social support to the caregivers of more functionally impaired elderly, family education to increase emotional support and physical assistance to the caregivers and broader and flexible application of social support such as increasing accessibility to the elderly daycare service with lower price may prove beneficial.