Abstract: This paper explores both the theoretical and empirical implications of parameter uncertainty for the optimal monetary policy reaction function. The responses of optimal real and nominal interest rate to the shock show gradualism when solely considering additive shock. If the last shock is not completely offsetted, superimposed effect will appear when a new shock hits the economic. The optimal real and nominal interest rate conservatism could be obtained under parameter uncertainty. The response of real and nominal interest rate to additive shock show gradualism when additive shock hits the economic