The changes in Thai population age–sex structure over time have resulted in an increasing proportion of elderly adults and, consequently, changes in living arrangements. In addition, the social and economic development that has motivated the rural-urban migration of labour forces has led to the transformation of rural households and communities, specifically resulting in larger numbers of elderly adults being left behind. This study aims to investigate the prevalence of depression among older adults in the Kanchanaburi Demographic Surveillance sites, and the factors related to depression. The analysis is based on the secondary data of Health and Social Support among Older Adults in the Kanchanaburi Demographic Surveillance Survey (Round1) 2006 (N=898). The findings reveal that as many as 27.5 percent of the studied older adults were living in a depressed condition. Considering the pattern of living arrangements, half of older adults experiencing depression were those living with their grandchildren, followed by those living with their spouses, and finally, those living with their offspring. The multiple regression analysis found that depression among older adults was significantly predicted by sex, age, educational level, occupation, financial status, chronic sickness, and sickness/disabilities of family members. The statistically significant positive relationship of the living arrangements of older adults to their depression was found among those living with their grandchildren. The analysis came up with the recommendations that interventions to promote improved family relationships between older adults and their grandchildren should be supported. Moreover, helping the elderly population should be the principles of governmental, non-governmental or any social institution.