Modern world development trends, the speeds of changes in technologies, social and economic systems have actualized the issue of effective ways of introducing and spreading innovations. The formation of a mathematically based, complex system of indicators makes it possible to objectively measure the speed of innovation implementation, the level of involvement of interested parties and the general transformation of the target socio-economic landscape. The purpose of the article is the formation of a mathematically based system of indicators for evaluating the effectiveness of the diffusion of innovations in socio-economic systems. The object of the research is the process of evaluating the diffusion of innovations in socio-economic systems. Methods used in the study: methods of scientific analysis and synthesis, induction and logical-analytical techniques, as well as methods of correlation, statistical factor analysis and center of gravity. The main hypothesis of the study is the assumption that the assessment of the effectiveness of the spread of innovations in socio-economic systems depends on a set of factors, the analysis of which allows identifying problem areas and improving mechanisms for solving problems. Presenting main material. The Global Innovation Index (GII) indicator system was used as the base of the study of the efficiency of innovation diffusion of socio-economic systems, as the database covers 130 countries of the world and is the most objective source of high-quality statistical information on innovative activity at the macroeconomic level. In the study, the construction of a system of indicators for evaluating the effectiveness of the diffusion of innovations was carried out based on the calculation data of the Global Innovation Index for 35 European countries for 2013-2023. The first stage of the formation of the system of indicators was the creation of the initial system of indicators and conducting a correlation analysis to eliminate multicollinearity between partial indicators. Based on this analysis, certain indicators whose correlation coefficients were in the interval [0.9–1.0] were excluded. At the second stage, using the statistical factor analysis method and making calculations using the StatSoft Statistics software, the initial system of selected indicators was aggregated to eleven factors that sufficiently describe the effectiveness of the diffusion of innovations at the country level. The study of factor loadings of indicators made it possible to determine the composition of partial indicators for each factor, the significance of which exceeds 70%. Among them, using the center of gravity method, representatives were determined for each influencing factor. Using a well-founded system of indicators, it is advisable to build a profile of the country's innovative diffusion effectiveness. Existing distortions make it possible to identify problematic aspects and direct efforts to their solution. The study carried out an analysis of the dynamics of innovation diffusion effectiveness in the form of petal diagrams for four European countries and proposed recommendations for stimulating their innovative activity. Diagnostics showed uneven development of the countries according to the studied factors in 2022-2023. The originality and practical significance the research consists in the fact that a mathematically based system of indicators of the effectiveness of the diffusion of innovations of socio-economic systems can be used for a comprehensive assessment, identification of problematic aspects and an increase in the level of diffusion of innovations in countries. Conclusions and prospects for further research: the system of indicators for evaluating the effectiveness of the diffusion of innovations in socio-economic systems is substantiated, which makes it possible to supplement the theoretical and methodological foundations of the management of innovative development processes. The system of indicators formed by the authors, which are representatives of each factor, should be used for an integral assessment of the effectiveness of the diffusion of innovations at the macroeconomic level, as well as for determining the problematic directions of the diffusion of innovations in socio-economic systems in order to direct the state innovation policy to their improvement.