The purpose of this study is to assess and compare the scale of the state sector in Russia, as well as the impact of the state ownership on the effectiveness of companies in Russia and BRICS countries. The study focuses on the major public companies, including state-ownership enterprises (SOEs). The methodology is based on the classification of the largest private and state-owned public companies, evaluation of SOEs’ contribution to key economic and financial indicators, regression analysis of the impact of state ownership on the financial performance. The state sector growth together with the unstable growth and volatile stock markets has been the trend in many economies since the crises of the last 20 years. The role of the state in corporate governance also increased. However, research on the performance of SOEs has become scarce, with virtually no reports from international financial organizations on the subject in the past few years. The issue of cross-country comparisons of the state role in the economy remains unsolved even thought it is of great theoretical importance in the discussions on models of state capitalism and development of methodology of state sector analysis, and is relevant for the management decisions in long-term strategies of socioeconomic development. The novelty of the study lies in the fact that the authors, using their own methods, collected and updated until 2021 indicators of the scale of the state sector, identified issues of assessment of the state sector, and used a unique database of companies from BRICS countries to study the performance of SOEs. The main results are the development of methodological approaches to the assessment of the state sector, updated state sector scale measures up to 2021, which show a continuing trend of growth. The authors have also shown how ambiguous are the existing solutions to measuring the size of the state sector and how large is the gap in estimates. The paper also shows that the state ownership had predominantly negative effect on companies’ performance in BRICS countries and South Korea. The main conclusion of the work is that it is necessary to develop a methodology that allows for an integrated assessment of government intervention on the economy, and to upgrade existing databases to increase corporate information transparency, both private and SOEs. This is especially important for the Russian economy, given the trend towards state sector growth. Such measures will improve the accuracy of state sector research and allow to improve the pace of economic recovery and ongoing monitoring