Sustainable development has become a prominent reference point in strategic planning and territorial improvement. Economic growth necessitates intensified efforts to utilize resources, often resulting in increased pressure on the environment and heightened social inequality. The application of sustainable development principles holds particular importance for urbanized territories. Assessing the regional sustainability integral indicator can help alleviate unequal socioeconomic development among municipalities. This indicator comprises indexes of the sustainability of individual territories. The authors propose the integral indicator as the arithmetic mean of indexes reflecting the sustainable development level of each component (economic, social, environmental). The authors applied this tool to municipalities in the Leningrad Region. Additionally, they conducted a ranking of municipal districts in the region based on the integral indicator. The leaders in sustainable development were the districts included in the St. Petersburg agglomeration. The authors suggest that a significant factor in the sustainable development of a territory is the presence of small enterprises, which possess the necessary flexibility for innovation in the social and environmental spheres. The authors propose distributing the elements of small and medium-sized enterprises (SME) potential according to the sustainable development factors of the region. The obtained data will enable the making of administrative decisions at the municipal and regional levels, including those related to the intensity and support for SMEs operating in relevant industries. This methodological approach to assessing the sustainability of the region and its internal municipalities, particularly concerning SMEs, can be utilized to make optimal administrative decisions related to government support for specific business areas.