This paper considers whether the development of cryptocurrencies poses any threat to the ability of central banks to control the value of their national currencies. Can the cryptocurrencies play the same role of actual currencies to impact the monetary policy? Despite all this inconvenience, the volume of transactions carried out using cryptocurrencies is still insignificant compared to those carried out using official currencies. Where the official money fulfills their main functions successfully when their value is sufficiently stable and there are no serious financial crises. While the cryptocurrencies are able to work as a medium of exchange only and they cannot perform the rest of functions of money successfully. They cannot be used as a unit of account or as a store of value due to its instability. In addition, the cryptocurrencies cannot control the inflation targeting, unlike the official currencies. However the future role of cryptocurrencies remains uncertain. The new technic “like a blockchain" will likely revolutionize finance in the future by conducting transactions faster, more securely and facilitate calculations that are beyond the capabilities of traditional computers. Therefore, we must keep an open mind about the new financial technology, not only because of the risks they pose but also for improving our lives.