Abstract Background: The disproportionate burden of more aggressive breast cancer subtypes among African American/Black women may stem from multilevel determinants. However, data are limited regarding the impacts of neighborhood social environmental characteristics among Black women. Methods: We evaluated the association between neighborhood-level socioeconomic status (nSES) and breast cancer subtypes in the Women's Circle of Health and Women's Circle of Health Follow-up Study, which included 1,220 Black women diagnosed from 2005 to 2017 with invasive breast cancer. nSES at diagnosis was measured using NCI's census tract-level SES index. We used multilevel multinomial logistic regression models to estimate the association of nSES with breast cancer subtypes [triple-negative breast cancer (TNBC), HER2-positive vs. luminal A], adjusting for individual-level SES, body mass index, and reproductive factors. We tested for interactions by neighborhood racial composition. Results: Compared with census tracts characterized as high nSES, the relative risk ratios (RRR) for TNBC were 1.81 [95% confidence interval (CI): 1.20–2.71] and 1.95 (95% CI: 1.27–2.99) for women residing in areas with intermediate and low nSES, respectively (Ptrend = 0.002). Neighborhood racial composition modified the association between nSES and TNBC; the highest relative risk of TNBC was among women residing in low nSES areas with low proportions of Black residents. Conclusions: Black women residing in socioeconomically disadvantaged neighborhoods may have an increased risk of TNBC, particularly in areas with lower proportions of Black residents. Impact: Places people live may influence breast tumor biology. A deeper understanding of multilevel pathways contributing to tumor biology is needed.