The aim of this paper is to find out determinants which affect liquid asset ratio of Czech and Slovak commercial banks. The data cover the period from 2001 to 2010. We consider four bank specific factors and nine macroeconomic factors. Results of panel data regression analysis showed that although Czech Republic and Slovak Republic have a lot in common, different factors determined banks′ liquid assets in individual countries. The liquid asset ratio of Czech banks increases with increase of capital adequacy, with depreciation of Czech koruna and with worsening quality of credit portfolio. Liquidity of Slovak banks decreases with size of the bank, with higher capital adequacy, higher bank liquidity and during periods of financial crisis. Liquidity of Slovak banks is also positively related to economic cycle.