AbstractAs well as breast cancer mortality, the income inequality in Brazil is different between Federative units, including between units of the same region. To assess the effects of the high-inequality of income on breast cancer mortality in Brazilian Federative Units, in the 2010 year. This is an ecologic study. Deaths from breast cancer in Brazilian women according to Federative units were obtained from the Department of Informatics of the Unified Health System. Mortality by breast cancer was estimated per 100,000 women and age-standardized by the direct method according to World Health Organization population. Income inequality was measured by the Gini index obtained from the United Nations Development Programme. The High-inequality of income was classified by the third tercile of the distribution from the Gini index of the Federative units. Univariate analysis was performed according to data normality. Linear regressions were performed by the stepwise backward method. The confidence level was 5%. Stata® (Stata Corp, LC) 11.0. was used. The High-inequality of income was associated with worse social and demographic indicators. The age-standardized breast cancer mortality was larger in the high-inequality of income Federative units. In the adjusted analysis, these Federative units presented a mean of 2 more deaths (ranging from the 0.4 to 3.7 deaths, r² = 0.79; p = 0.018) by breast cancer per 100,000 women when compared to the Federative units without high-inequality of income. In the Brazilian Federative units, the high-inequality of income was associated with age-standardized breast cancer mortality more.