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Macroeconomic performance has improved in many countries in the world in the last fifteen years or so. Much of the literature has concentrated on how central bank independence, inflation targeting regimes, and currency :::union:::s have contributed to improving the effectiveness of monetary policy and hence macroeconomic performance. Since the financial system is a key component of the monetary transmission mechanism, we study how a country’s financial development affects monetary policy efficiency in 28 developed and developing countries within 1995-2006. Specifically, our objective is to derive monetary policy efficiency measures (PEMs) - derivative from Krause and Rioja- for 28 Developed and developing countries and analyze the impact that the size and depth of the banking sector and the capital sector have on policy performance. In our empirical analysis we use three financial development measures: private credit, liquid liabilities, and a financial aggregate index that comprises banking and stock market measures. The Results of model estimation with generalized method of moments (GMM) technique, shows that financial development with mentioned indicators has a positive and significant effect on monetary policy efficiency. Also supervision in central bank independency and inflation targeting regimes -as control variables- has positive and significant effect on monetary policy efficiency. This result doesn’t make a difference whether the country is developed or developing and in the both of them more developed financial markets, controlling the central bank independency and applying inflation targeting regimes, significantly help to achieve a more efficient monetary policy.