Background and objective: Women living in economically segregated areas are less likely to receive adequate breast cancer care and access community resources, which may heighten breast cancer mortality risk. We investigated whether the conditional cash transfer programme Bolsa Família (BFP) could mitigate the detrimental effects of living in segregated areas on breast cancer mortality. Methods: We analysed data on 20,680,930 adult women from the 100 Million Brazilian cohort, linked to nationwide mortality registries (2004-2015). The association between womens’ residential segregation at the municipality level (using the dissimilarity index in tertiles: low/medium/high) and breast cancer mortality was analysed using Poisson regression adjusted for age, race/ethnicity, education, area of residence (rural/urban), municipality’s area size and population density. Multiplicative interactions between residential segregation and BFP receipt (yes/no) were assessed. Results: Breast cancer mortality rates were greater among women living in high (adjusted Mortality rate ratio=1.18, 95%CI 1.12-1.23) and medium (1.07, 1.03- 1.12) vs low segregated municipalities. Women not receiving BFP had higher breast cancer mortality rates (1.12, 1.08-1.17) than BFP recipients. Stratified analysis by BFP receipt showed that among BFP recipients, women living in high vs low segregated municipalities had a 12% (1.12, 1.06-1.19) greater risk of dying from breast cancer; among non-recipients of BFP, the risk of dying for women living in high vs low segregated municipalities was 23% higher (1.23, 1.14-1.33) (P for interaction=0.008). When stratifying by the time in years receiving the benefit, associations between segregation and mortality were stronger for women receiving BFP benefit for less time (<4 years:1.10, 1.01-1.20; 4-7 years: 0.97, 0.89- 1.07; 8-11 years:1.09, 0.95-1.25) (P for interaction<0.001). Conclusion: Place-based inequities in breast cancer mortality due to residential segregation might be attenuated through the BFP, possibly by improving women’s familial income and access to preventive cancer care services, leading to early detection and treatment and ultimately reducing mortality.