The article considers the transactional sector as an important component of the economic system at any level of the hierarchy. The existing interpretations of the transactional sector of the economy are analyzed. The authors focus attention on the gap between the concept of transactional isolation sector and the need to measure transaction costs in the economic system. The conclusion is made about the absence of clear criteria for the allocation of transaction sector in the regional economy. Transactional activity is proposed as a criterion for determining the nature and composition of the transaction sector. The description of the purposes, subject matters and scopes as well as issues of transactional activity is presented. The composition of the transaction sector is determined at the regional level as a set of institutional units from different fields of activity: financial, trade, information and intellectual, as well as public administration. A structural-functional approach to the analysis of the impact of the transaction sector on the economy of the region is proposed. In its framework, the features of functions of the transactional sector in the context of its structural components are considered. The allocation of the function of the transactional sector is made based on the analysis of functions of institutions. The content of system-forming, coordinating, distributing, integrating and information functions of the regional economy transaction sector is revealed. The authors have developed a model characterizing the impact of transaction sector on the economy of the region through the implementation of these functions.