Purpose: The aim of this study was to evaluate the level of self-care adherence in the elderly with diabetes mellitus (DM) who have lived alone, and to investigate the association between health literacy, diabetic knowledge and self-care adherence. Methods: Descriptive research using the cross-sectional approach was conducted. Data was collected by using a convenience sampling of 201 participants who aged sixty-five years old or more and have lived alone. Statistical analysis was conducted by using an independent t-test, one-way ANOVA, Scheffe? test, Pearson correlation coefficient and stepwise multiple regression analysis. Results: Mean scores of health literacy, diabetic knowledge and adherence of self-care were 4.41±3.54 points out of a possible 12, 6.22±2.55 points out of a possible 15, 58.56±17.28 points out of a possible 112, respectively. Adherence of self-care showed a statistical association with health literacy (r=.26, p<.001) and diabetic knowledge (r=.30, p<.001). Statistically significant factors in the regression model were monthly income, diabetic knowledge and exercise. Conclusion: The level of self-care adherence in the elderly with diabetes living alone was relatively low. Diabetic knowledge was an important factor to improve the level of self-care adherence for the elderly with diabetes living alone.