The novel coronavirus disease 2019 (COVID-19) spread rapidly worldwide. Nursing home (NH) residents are the most vulnerable high-risk population to infection. Professional registered nurses' (RNs') infection control is irreplaceable. We used a secondary data analysis method using the government's senior citizen welfare department large data set about all NHs (N = 3,389) across Korea between January 20 and October 20, 2020. Bed size positively associated with the mortality rate (No. of COVID-19 resident deaths / No. of total residents) (p = .048). When the proportion of RNs to total nursing staff was higher, the infection rate was 0.626% lower (p = .049), the mortality rate was 0.088% lower (p = .076), the proportion of confirmed COVID-19 cases per resident out of the total number of NHs was 44.472% lower (p = .041), and the proportion of confirmed COVID-19 deaths per resident out of the total number of NHs was 6.456% lower (p = .055). This study highlighted nurse staffing criteria and suggests that increasing RNs in NHs will reduce infection and mortality rates during the COVID-19 pandemic. We strongly suggest NHs hire at least one RN per day to properly function, and a minimum of four RNs to provide a fully competent RN workforce in long-term care settings in Korean NHs.