The crisis has thrown the disorder on the effectiveness of the monetary policies. Indeed, the intensity of the financial crisis and the downward pressure it exerted on price stability has prompted many central banks to fix their interest rate at levels historically low. In September, the Federal Reserve conducts a decline in its rate to reach in December 2008, a floor close to zero, The Central Bank, for its part, has begun the process of falling interest rates in October 2008; which is continued until reaching a rate of 0.75% in July 2012. In a crisis, the fixation of the interest rate by the Central bank which is close to the 0% it is essential in order to stimulate economic activity, but, once the floor is reached, the risk of liquidity trap occurs, this leads monetary authorities to rethink their monetary policy and resort to others means of action other than further decline in interest rates. The purpose of this communication is to know whether the adoption by the central banks (European Central Bank and Federal Reserve case) of unconventional monetary policies, especially the policy of quantitative easing, has it enabled expansion of loans to households and finance companies, and therefore, contributed to an economic growth?