With ongoing global outbreak of coronavirus disease 2019 (COVID-19), management of exposure events is a concern. Long-term care hospitals (LTCHs) are especially vulnerable to cluster outbreaks, since it is difficult to find facilities and healthcare personnel for their separate isolation care in a large outbreak situation. Although several drugs have been proposed as treatment regimens, there are no data on the effectiveness and safety of post-exposure prophylaxis (PEP) for COVID-19. After a large COVID-19 exposure event in a LTCH in Korea, PEP using hydroxychloroquine (HCQ) was conducted to 211 persons including 189 patients and 22 careworkers, whose baseline polymerase chain reaction (PCR) tests for COVID-19 were negative. PEP was completed in 184 (97.4%) patients and 21 (95.5%) careworkers without serious adverse events. At the end of 14 days of quarantine, follow-up PCR tests were all negative. Based on our experience, further clinical studies would be conducted for COVID-19 PEP.