The article discusses the socio-economic development of countries in integration associations of the North-South and South-South types - the European Union (EU) and Eurasian Economic Union (EAEU). One of the most serious impediments to economic integration is inequality, which associations try to address through special programs and financial mechanisms. The study relies on methods of comparative analysis and modeling. The empirical data were provided by the statistical databases of the World Bank, EU, OECD, Human Development Report and the EAEU Statistical Report. We propose to modify the “center-periphery” model for analysis of socio-economic development of integrated countries, in particular member states of the EU and EAEU. In 2009-2018, eight EU countries improved their positions and the most stable countries in the integration associations are Austria, Germany, Denmark, the Netherlands and Sweden; the least stable countries are Armenia, Greece, Kyrgyzstan, Poland, Romania and Croatia. Despite the long and active financial support to developing countries, there is still a considerable imbalance in socio-economic development of countries within the associations and this imbalance increases during the recession period.