The paper researches the peculiarities of forming and functioning of business support instruments in a region in conditions of authorities’ decentralization. The research aims to analyze the specifics of application of business support instruments in Ukrainian regions and to reveal the problems and challenges of entrepreneurship sector transformation in this framework. The scheme of classification of the business support instruments is suggested and four basic groups of instruments are defined, in particular: administrative and legal, financial and economic, informational and consulting, social and cultural. Major indicators of entrepreneurship sector development at the level of Ukrainian regions are analyzed. Analysis of methodical approaches to evaluation of regions and their rankings by the entrepreneurship development indicators is conducted. In particular, the paper researches the adapted methodology of World Bank that stipulates the evaluation of the ease of doing business (entrepreneurship activity) across the five directions of cooperation of entrepreneurs with local authorities. The most important directions of organizational and economic development that reduce the problems of institutionalization of business support instruments at regional level are outlined,in particular: introduction of new and substitution of existing organizational and management forms of activity of business support structures; preserving and renewal of staff and management potential; investment attraction and stimulation of economic activity of entrepreneurship sector; introduction of the new forms of funding and assistance to business at the level of communities; promotion of communities’ role in maintenance of entrepreneurship sector functioning in the regions; improvement of information provision and communication between the authorities and business. Efficient institutionalization of the instruments of business support and development in a region should take place on the basis of mesoeconomic approach to the development of the new forms of doing business, which requires further research in terms of substantiation of conceptual provisions of the development of region’s territories through stimulation of entrepreneurship activity of community’s residents and forming of creative local clusters.