The function of money plays an essential and indisputable role in the development of trade. Typically, banknotes and coins have always been introduced by central authorities. Emerging after the 2008 crisis, however, Bitcoin, considered to be the original cryptocurrency, contributed to money in an unprecedented dimension as it is the first decentralized peer-to-peer payment network. Cryptocurrencies are in constant interaction and the casualty relationship, among other variables, with Brent Oil. This study attempts to investigate the relationship between Bitcoin, Ethereum and Brent Oil price movements using 210 daily data from 10.12.2019 to 01.10.2020, featuring the period of the start and the spread of the COVID-19 pandemic. In this study, the casualty relationship among Brent Oil, Bitcoin and Ethereum was examined with the Granger Causality test. As a result of the study, a bidirectional casualty relationship is determined between Brent Oil and Ethereum. However, a one-way causality relationship is found between Brent Oil and Bitcoin. On the other hand, there is no causality relationship between Ethereum and Bitcoin.