This paper aims to empirically examine the factors affecting the capital adequacy ratio by using the data collected from the audited financial statements of 24 joint-stock commercial banks in Vietnam over the period from 2009 to 2019 and adopting the generalized least squares estimation method. The results show that financial leverage, deposits from clients, loans to customers, liquidity, and profitability negatively affect the capital adequacy ratio. In addition, the paper also recognizes that the difference between the actual capital adequacy ratio and the prescribed minimum ones can be explained by the negative influence of bank size, financial leverage, loans to customers, liquidity, and profitability. The study provides empirical evidence and useful information for bank managers to make rational decisions in maintaining and adjusting their level of capital adequacy.