Breast cancer (BC) is one of the leading causes of cancer deaths in females in South America. This study aims to examine the BC burden in 12 South American countries between 1990 and 2019. The estimates of BC burden and risk factors were procured from the Global Burden of Disease 2019 study for the period 1990-2019. Development levels of countries were gauged using socio-demographic index (SDI). Decomposition analysis was employed to categorizethe change in incidence between 1990 and 2019 into three factors: population growth, population aging and age-specific incidence rate. Estimated annual percent changes were calculated for each country and bivariate association between country-level age-standardized rates and SDI was examined using pooled regression. The age-standardized rates of breast cancer were the highest in Uruguay [incidence: 72.65 per 100,000 (55.79-92.57); mortality: 29.97 per 100,000 (27.54-32.27); disability-adjusted life years (DALYs: 810.49 per 100,000 (746.22-884.55)] and lowest in Peru [incidence: 27.63 per 100,000 (20.44-36.85); mortality: 10.79 per 100,000 (8.14-14.11); DALYs: 318.27 per 100,000 (234.47-421.16)]. Mortality-to-incidence ratio (MIR) across countries varied from 0.30 in Colombia to 0.55 in Bolivia in 2019. SDI had a positive and strong association with age-standardized incidence rate [Formula: see text] and weaker positive association with age-standardized mortality rate [Formula: see text] and age-standardized DALYs rate [Formula: see text]. Most countries experienced more than 70% increase in incident cases owing to population aging and age-specific incidence rates. Alcohol Use, diet high in red meat and smoking contributed the maximum DALYs in most countries in 2019 whereas DALYs due to high body-mass index and high fasting plasma glucose increased most substantially between 1990 and 2019. With increasing incidence, high MIR and rising BC burden due to modifiable risk factors, several public health interventions are required in South America focusing on prevention, BC awareness among general public, cost-effective early detection and treatments that suit the socio-economic setup of South American countries.