Purpose: This study was conducted in order to investigate the physical activities of vulnerable low-income middle-aged people and their associated factors. Methods: From a health behavior survey of 1,000 vulnerable low-income subjects from a public health center in a metropolitan city, a secondary analysis was conducted for 332 respondents who ranged in age from 40 to 64. Results: The prevalence of walking activity was 45.2% and that of moderately intense physical activity was 9.9%. Prevalence of walking activity showed a significant association with marital status (divorce/widowed/separated, OR=2.263), drinking (drinker, OR=0.430), and CES-D score (over 21, OR=0.434). Prevalence of moderately intense physical activity was greater in subjects who had two chronic diseases, compared with those who had no chronic diseases (OR=3.713). Conclusion: Findings of this study suggest a need for implementation of strategies to improve moderately intense physical activity of low-income, middle-aged people. Also, in addition to studies on socio-demographic and health status and their associations with physical activity, further studies of related factors affecting physical activity, such as self-efficacy, social support, and social networks as internal and external resources, are needed.