This paper investigates the effect of the COVID-19 pandemic on firm performance, cash flows, cash holdings and leverage. Using quarterly data of 415 firms listed in the Vietnamese stock market, this study employs the t-test method to compare firms' outcomes between the two main periods, including the happening of COVID-19 period (from Q1-2020 to Q1-2021) and the normal period (from Q1-2010 to Q4-2019). The results show that the pandemic significantly impairs firm performance and its cash flows. In addition, firms are found to hold more cash and reduce their leverage ratios to combat the disease outbreak. This study also provides supportive evidence that the COVID-19 pandemic may not necessarily affect firms across industries equally.