The COVID-19 pandemic continues to overwhelm health systems across the globe. We aimed to assess the readiness of hospitals in Nigeria to respond to the COVID-19 outbreak. Between April and October 2020, hospital representatives completed a modified World Health Organisation (WHO) COVID-19 hospital readiness checklist consisting of 13 components and 124 indicators. Readiness scores were classified as adequate (score greater than or equal to80%), moderate (score 50-79.9%) and not ready (score <50%). Among 20 (17 tertiary and three secondary) hospitals from all six geopolitical zones of Nigeria, readiness score ranged from 28.2% to 88.7% (median 68.4%), and only three (15%) hospitals had adequate readiness. There was a median of 15 isolation beds, four ICU beds and four ventilators per hospital, but over 45% of hospitals established isolation facilities and procured ventilators after the onset of COVID-19. Of the 13 readiness components, the lowest readiness scores were reported for surge capacity (61.1%), human resources (59.1%), staff welfare (50%) and availability of critical items (47.7%). Most hospitals in Nigeria were not adequately prepared to respond to the COVID-19 outbreak. Current efforts to strengthen hospital preparedness should prioritize challenges related to surge capacity, critical care for COVID-19 patients, and staff welfare and protection.