This article examines the impact of ethnodemographic characteristics on the level of well-being in the Soviet republics. The author analyzes demographic, anthropometric, and socio-economic indicators, revealing a close correlation between family size, fertility rates, anthropometric parameters such as average male height, and nutritional models. The study identifies two major ethnodemographic clusters: a European cluster characterized by smaller families and higher anthropometric indicators, and a Transcaucasian-Central Asian cluster marked by larger families and lower levels of physical development and protein intake. Within these clusters, several intermediate and significantly changing regions emerge in the late Soviet period. The article highlights contradictory processes of both convergence and divergence among national republics across a number of indicators. Many of these differences are rooted in enduring cultural, religious, and ethnic traditions, which persisted despite the overarching processes of industrialization and urbanization. Particular attention is given to the concept of “demographic burden” — the ratio of dependents to the working-age population — which varied greatly across republics. A high demographic burden in regions with larger families created additional economic pressure, limiting opportunities for improved quality of life. Conversely, the lower demographic burden in the European part of the USSR contributed to economic growth and rising living standards. The article emphasizes that the ethnodemographic factor is one of the key elements influencing socio-economic development and quality of life in the USSR. © 2025, Saint Petersburg State University. All rights reserved.