The stability of money demand has been studied by many economists and for many countries considering the domestic interest rate and income level as determinants of this. However, when the economies begin to open to the world, the question arises how affect external variables as international interest rates and the exchange rate to the demand for money? So some models have been elaborated which seek to explain the demand for money in open economies. This paper seeks precisely the existence of a stable money demand in an open economy context. For this situation has used the Cash-in-advance model for open economies as a theoretical basis. For verification empirical has been used cointegration and error correction models were in fact there is a stable function in the long term. In addition it was found that the external sector variables are significant in determining the demand for money to Peruvian case.