BACKGROUND/OBJECTIVES: Inner-city Black women may be more susceptible to posttraumatic stress disorder (PTSD) than White women, although mechanisms underlying this association are unclear. Living in urban neighborhoods distinguished by higher chronic stress may contribute to racial differences in women's cognitive, affective, and social vulnerabilities, leading to greater trauma-related distress including PTSD. Yet social support could buffer the negative effects of psychosocial vulnerabilities on women's health. METHODS/DESIGN: Mediation and moderated mediation models were tested with 371 inner-city women, including psychosocial vulnerability (i.e., catastrophizing, anger, social undermining) mediating the pathway between race and PTSD, and social support moderating psychosocial vulnerability and PTSD. RESULTS: Despite comparable rates of trauma, Black women reported higher vulnerability and PTSD symptoms, and lower support compared to White Hispanic and non-Hispanic women. Psychosocial vulnerability mediated the pathway between race and PTSD, and social support moderated vulnerability, reducing negative effects on PTSD. When examining associations by race, the moderation effect remained significant for Black women only. CONCLUSIONS: Altogether these psychosocial vulnerabilities represent one potential mechanism explaining Black women's greater risk of PTSD, although cumulative psychosocial vulnerability may be buffered by social support. Despite higher support, inner-city White women's psychosocial vulnerability may actually outweigh support's benefits for reducing trauma-related distress.