Using data from the 2015 Korea Welfare Panel Study, we examined the predictors of psychological well-being (life satisfaction and depression) of single elderly people living alone across development stages (young-old, mid-old, and old-old) and suggested implications for elderly policy. For this purpose, we selected 1,364 elderly people who lived alone but preserved their family relationships, and were 65 years of age or older. Separate analyses were conducted for the three groups of single elderly people living alone. Overall, the psychological well-being of single elderly people living alone was higher than moderate level, and they were generally satisfied with their everyday lives and less depressed. However, there were group differences: the young-old group was more satisfied than the old-old group with in their everyday lives and less depressed than the mid-old and old-old groups. In the young-old group, life satisfaction was significantly associated with subjective health, non-physical conflict with family, disposal income, house ownership, dietary deficiency, cost of living, and public pension. In addition, depression was significantly associated with subjective health, non-physical conflict with family, dietary deficiency, and physical conflict with family. In the mid-old group, life satisfaction was significantly associated with subjective health, housing non-physical conflict with family, disposal income, and dietary deficiency. Depression was significantly associated with subjective health, housing deficiency. In the old-old group, life satisfaction was significantly associated with subjective health and non-physical conflict with family. Depression was significantly associated with subjective health. Therefore, ‘health’and ‘family’are important key concepts to consider when making elderly policy.