Poor mental health significantly impacts people with HIV (PWH) and those who drink alcohol. Limited data exist on the combined effects of social determinants of health (social vulnerability) on mental health in PWH with unhealthy substance use. We investigated the relationship between social vulnerability and poor mental health in PWH and whether this relationship differed by race/ethnicity. We conducted a cross-sectional analysis using data from the Boston ARCH Cohort among PWH with current or past unhealthy substance use. We created a 23-item social vulnerability index (SVI) using a deficit accumulation approach comprised of social determinants of health indicators. We estimated whether higher SVI score is associated with anxiety and depressive symptoms using logistic regression analysis. Among 251 participants with a mean age of 52 (SD = 10) years, 67.3% were male, 52% Black, 21% Hispanic, 19% White, and 73% unemployed. The SVI had a mean of 9.30 (SD = 3.4) with a 1.5-18 range. Nearly two in five persons reported past month heavy alcohol use and 35% illicit drug use. The prevalence of anxiety and depressive symptoms was 34.4% and 54.2% respectively. Higher SVI score was associated with anxiety symptoms (adjusted odds ratio [aOR] = 2.01, 95% confidence interval [CI] 1.46, 2.76, p ≤ 0.001), and depressive symptoms (aOR = 2.42, 95% CI 1.74, 3.36, p ≤ 0.001). Race/ethnicity did not moderate the relationship between SVI and each mental health outcome. SVI was significantly associated with poor mental health across racial/ethnicity groups in this cohort. Interventions that address social vulnerability may improve well-being and quality of life for PWH.