Background: Racial disparity in breast cancer (BC) goes beyond access to care. Biology of HER2- and Triple Negative (TNBC) tumors has been shown to differ between African Americans (AF) and Caucasians (CF), contributing to survival difference. Additionally, tumor infiltrating lymphocytes (TILs) incurred favorable response to neoadjuvant therapy in ER- and TNBC. We hypothesized that TIL composition of immune microenvironment (IME) differs between AF and CF, potentially explaining such biologic disparity. Methods: Using The Cancer Genome Atlas (TCGA), we applied recently described gene expression deconvolutional algorithm CIBERSORT, estimating 22 IME cell proportions. Clinical and PAM50 data were accessed from XENA. Cytolytic activity appended from Rooney et al. Results: 183 AF Pts had worse disease-free survival (5-year DFS 21% vs. 26%, HR 1.67[1.02-2.73]) and cumulative incidence of disease (sHR 1.75[1.09-2.81]) compared with 752 CF Pts, adjusted for age and stage. DFS gap was most prominent in Basal subtype (HR 3[1.03-9.1]). Certain TILs impacted DFS and OS. Higher CD8 T cell fractions improved DFS and OS (HR 0.75[0.59-0.9] and 0.8[0.65-0.95]). Higher activated NK and γδT cell fractions predicted better DFS (HR 0.64 and 0.06). M2 macrophages incurred poor DFS (HR 11.6[1.07-126]). On adjusting for race, activated NK, γδT and M2 macrophage retained respective outcome, but not CD8 T cells. Regulatory T cells (Tregs) did not impact DFS or OS. Comparing AF to CF IME, CD8 T cells were higher in ER+ Pts only. Tregs were higher in whole cohort, Basal and TNBC subtypes. T follicular helper cells were higher in TNBC/Basal, and activated dendritic cells were higher in ER+/Luminal subtypes. Higher memory B, Plasma cells and Macrophages were seen in all subtypes except Basal (p < 0.01). Cytolytic activity was similar between AF and CF. It correlated with γδT cells (r² 0.41, 0.49 in AF) and memory CD4 cells (r² 0.4, 0.3 in AF), but not DFS or OS. Conclusions: IME in BC significantly differs by race, with AF having more Tregs in Basal/TNBC, and more CD8 T cells only in Luminal subtypes. This IME in Basal subtype (and TNBC phenotype) can explain independent worse outcome for this cohort. Incomplete deconvolution of heterogenous Tregs might explain lack of outcome correlation.