This study examined the social determinants of health inequality in urban Brazil and Nigeria, focusing on healthcare access, health behavior, and environmental factors. A comparative quantitative design was adopted using secondary data from the 2019 Brazil National Health Survey, the 2018 Nigeria Demographic and Health Survey, WHO air quality data, and World Bank indicators. The findings show that urban residence does not guarantee equal health opportunities in either country. Brazil recorded stronger healthcare access indicators, including higher doctor consultation and continuity of care, but income-based inequality remained visible, especially in private health plan coverage. Nigeria showed greater healthcare access barriers, particularly among women, with cost, distance, and limitedservice availability affecting care use. Health behavior also differed: Brazil’s urban health risks were more associated with tobacco use, alcohol consumption, unhealthy diet, and noncommunicable disease risk, while Nigeria’s indicators were more linked to reproductive health, family planning, and maternal care. Environmental inequality was also evident, with Brazil showing higher piped water access and lower PM2.5 exposure, while Nigeria experienced higher air pollution and incomplete household infrastructure. The study concludes that urban health inequality in both countries is socially produced through unequal access to healthcare, income, education, housing, sanitation, and environmental protection. Reducing these inequalities requires integrated policies combining healthcare reform, poverty reduction, health education, environmental protection, and inclusive urban planning