Purpose: This study aimed to assess the levels of and relationships among health literacy, knowledge about diabetes, and self-care activities in the Korean low-income elderly with diabetes and to identify factors influencing the self-care activities of this vulnerable population. Methods: This study surveyed a total of 151 low-income elderly patients with diabetes registered at 16 Visiting Health Care Services in B City, Korea. Health literacy was measured with the Newest Vital Sign. Diabetes knowledge was measured with the Diabetes Knowledge Test. The Summary of Diabetes Self-care Activities Questionnaire was used to assess diabetes self-care activities. A stepwise multiple regression analysis was conducted to identify significant factors influencing diabetes self-care activities in these patients. Results: In the regression model, diabetes knowledge (${eta}=.322$, p<.001), exercise (${eta}=.337$, p<.001), and experiences of diabetes education (${eta}=.241$, p=.001) were significantly associated with increased diabetes self-care activities in low-income elderly patients with diabetes when gender, education, health literacy, and subjective health state were controlled. Conclusion: To improve diabetes self-care activities in the low-income elderly with diabetes, it is important to develop a customized program considering their knowledge, exercise, and diabetes education experience.