This paper examines the regulation of Interest Rate Risk Management of the Banking Book in the Czech and Slovak banking sectors. We provide modelling of bank balance sheets in terms of regulatory requirements. The contribution of our paper is two-fold. First, we identify the key business drivers of Interest Rate Risk of the Banking Book of the Czech and Slovak banking sectors. Second, when comparing the interest rate risk of the banking book of both banking sectors, we find that major banks in both sectors report a higher interest rate risk from their client liabilities than from client assets. This fact implies that the banks are exposed to the risks inherent in rising interest rates. We find that the interest rate risk exposure of the Czech and Slovak banks is relatively high, and therefore, the potential contagion risk for large foreign owners with subsidiaries in both countries is not negligible.