Background: Older adults who live alone are less physically and emotionally healthy and report higher levels of depression relative to those who do not live alone. Suicide is the most problematic health issue reported by older adults who live alone. In particular, vulnerable older adults who live alone experience difficulty obtaining self-care and medical services; therefore, early detection of depression is difficult, and there are few opportunities to implement suicide prevention strategies in this population. In addition, social support for depression is an important factor affecting illness and economic vulnerability in older adults who live alone. Purpose: This study aimed to examine the relationship between depression and suicidal ideation in vulnerable older Korean adults with hypertension and to explore the mediating effect of social support on this relationship. Methods: The study used a cross-sectional design. Vulnerable older adults who were 65 years old or older with hypertension and who received home visit services from a public health center were invited to participate. The participants completed structured questionnaires, including the 15-item Short-Form Geriatric Depression Scale, 12-item Multidimensional Scale of Perceived Social Support, and 19-item Scale for Suicidal Ideation, and provided information regarding their demographic characteristics, health status, and economic status. Descriptive and correlation analyses were performed to examine the correlations among these variables. The three-step regression analysis method proposed by Baron and Kenny was used to examine the mediating effect of social support. Results: The mean depression, social support, and suicidal ideation scores of participants were 23.64 (+/- 2.04), 35.94 (+/- 15.40), and 7.80 (+/- 7.73), respectively. In addition, depression was negatively correlated with social support (r = -.27) and positively correlated with suicidal ideation (r = .21), whereas social support was negatively correlated with suicidal ideation (r = -.35). Social support mediated the relationship between depression and suicidal ideation (Z = 2.69). Conclusions: Social support was identified as an important variable for older adults with chronic illness who lived alone. Interventions that include social support hold the potential to reduce depression and suicidal ideation in this population.