In world practice, support and promotion of social innovations are one of the effective areas of public policy. This is due to a wide range of tasks that lie in the field of social innovation: from resolving problems of employment, education, environment, increasing the availability of health care to the development of agriculture, energy and transport. At the same time, the key factor in their implementation is the presence of an enabling environment and active interaction of interested parties (authorities, business, civil society structures, scientific and educational organizations, social entrepreneurs, etc.), all of which form a social innovation ecosystem. In this regard, an analysis of the situation in this area is becoming an important dimension for both science and governance. Taking into account the relevance of the development of social innovations, it seems possible to identify the social innovation subsystem within the regional innovation subsystem and consider it in terms of the ecosystem approach, i.e. as an ecosystem. However, owing to the limited information on social innovations in Russia, especially at the regional level, evaluating the development of socio-innovative ecosystems is associated with a number of difficulties, which leads us to the need to find relevant tools. In this article we proposed an original approach based on the index method to address this issue. The suggested research tools were tested on data for 2018 for the regions of the Northwestern Federal District of Russia. The results of the study showed uneven development of the environment for the implementation of social innovations and the potential for interaction between the subjects of the regional economy, which can participate in their introduction and promotion. Using the matrix approach, we identified six possible types of regions by the level of development of social innovation ecosystems. In 2018, four types of territories were established, formed on the basis of clustering regions with a high, medium, and low level of development of social innovation ecosystems’ components. The research determined the main challenges in the future of social innovation ecosystems in Russia and the directions to improve the current situation.