Abstract
In achieving price stability as the primary objective of monetary policy, the National Bank of Serbia uses the key policy rate as the main instrument of monetary policy, while other instruments have a supporting role - contribute to a smooth transmission of the key policy rate on the market, as well as the development of financial markets. However, because the conditions in which economic and financial system of the Republic of Serbia works, transmission mechanism of monetary policy is conducted mainly through the exchange rate channel, while the channel of interest rates almost did not work. The great impact the exchange rate channel is determined by the great influence of the single currency euro and the ECB on our country. Therefore, the aim of this paper is to analyse the efficiency of the key policy rate as a monetary policy instrument, because in recent years the primary instrument receives a secondary character in the monetary regulation.