Theoretical and methodological foundations of institutional policy define reduction of uncertainty in activities of organizations and individuals as the main task of financial institutions by establishing stable mechanisms of interaction between participants in public relations. Coordination of economic interests at all levels is performed by both formal and informal institutions, while creation and modification of formal institutions largely depends on the informal influence of representatives of various social macrogroups. The list of the most important macroeconomic institutions includes: institutions of macroeconomic regulation; market institutions; monetary institutions, fiscal institutions, investment institutions; institutions of law; institutions for regulation of foreign economic activity. Whereas, the importance and peculiarities of financial policy in the institutional system determine the special importance of financial institutions, primarily in implementation of measures aimed at ensuring sustainable social and economic development. The paper dwells on practice of functioning of the financial system of Belarus. The value of a unique mega-regulator for financial transactions, exchanging assets and risks has been determined. It has been substantiated that creation of such a supranational body is possible subject to formation of an integrated financial market for the EAEU member states. Impact of the main instruments of financial policy (Belarusian ruble exchange rate, refinancing rate, money supply, required reserves of second-tier banks, monetary policy stability, informal influence measures, agreements, transactions, open market operations, tariffs, duties, restrictions, decrees, orders, guarantees) on the national economy has been considered, proposals for improving financial instruments within the framework of the current institutional mechanism has been substantiated. Use of the proposed results and proposals in practice for improving institutional mechanisms, including a range of official regulations and informal institutions, will promote improvement of the situation with the balance of payments, assessment of fiscal risks and problem assets.