Purpose: The aims of this study were to identify depression rates depending on the sex among elderly people living alone and to compare depression-related ecological system factors between two sex groups.Methods: A cross-sectional study was conducted using secondary data from the 7th Korean Longitudinal Study of Aging survey in 2018. A total of 893 elders living alone were included (152 men and 741 women). Hierarchical logistic regression was used to identify depression-related ecological system factors depending on the sex.Results: Men had significantly higher rates of depression (28.6%) than women (24.0%, p<.001). Depression-related ecological system factors in elderly women were higher educational level, poor subjective health status, impairment of instrumental activities of daily living, low satisfaction with children’s relation, financial based on children’s support, and rare meetings with close people. However, relation satisfaction with children was the only relevant depression-related ecological system factor in the men’s group.Conclusion: Our study findings show that depression-related ecological system factors vary depending on the sex of elderly people living alone. Thus, mental health professionals should provide sex-specific interventions to develop or implement depression-prevention strategies for the elderly living alone depending on the sex.