Although Vietnam has been successful in the fight against the first wave of COVID-19, domestic outbreaks have continued to occur. Given university students constitute a significant proportion of the population in Vietnam, to improve the prevention and control of COVID-19 in Vietnam and comparable countries, we examined their knowledge, attitude, and practice (KAP) towards face mask use which is an important preventive measure and the association between the levels of COVID-19 knowledge and KAP towards face mask use. A cross-sectional survey was conducted on all students studying at Phenikaa University, Hanoi, using a self-developed questionnaire consisted of 42 questions regarding KAP towards face mask use as well as reuse of cloth mask, and COVID-19 knowledge. Among 728 participants, 40.9% (298/728) were male, 63.2% (460/728) were from health-related faculties, 46% (335/728) lived in urban areas, and 51.9% (378) had good levels of COVID-19 knowledge. Regarding face mask, most (89.7%, 653/728) participants had good knowledge scores, 72.8% (530/728) had positive attitudes, and 76.5% (557/728) had good practice scores. The most common types of masks used were surgical mask (57.6%, 419/728), followed by non-antibacterial cloth mask (23.1%, 168/728). Among 168 participants using non-antibacterial cloth mask, 43.5% reused masks (73/168), of whom 6.8% (5/73) did not wash their masks at least daily. Face mask use knowledge was statistically associated with COVID-19 knowledge (P < 0.001). Face mask use attitudes were statistically associated with education levels (P = 0.02), and COVID-19 knowledge (P < 0.001). Practice of face mask use was statistically associated with gender (P = 0.03), geographical distribution (P = 0.04), academic majors (P = 0.02), and COVID-19 knowledge (P = 0.01). The levels of KAP towards face mask use among Vietnamese university students are high. It is important to continue to enforce the mass masking policy, together with the ongoing community education with an emphasis on the route of COVID-19 transmission and how correct face mask use can stop the spread. To ensure the effectiveness of face masks, there is an urgent need to educate the community regarding the procedures for cloth masks re-use.