In this paper, we empirically examine the impact of key interest rate on national and sector economic growth. Using Tunisian quarterly data in the period 2000-2018, we estimate, in the first step, the long term relationships through VECM analysis and, in the second we enrich our study by introducing variables of interaction. We find that key interest rate significantly and positively influences national and sector economic growth and negatively affects the inflation. In specific, our results show that the economic crisis and the approved credits respectively influence negatively and positively the link between key interest rate and Tunisian economic growth. Finally, we show that the impact of changes in monetary policy is weaker in crisis period and improved by the bank credit rises.