Objectives: No data were available about in-flight transmission of SARS-CoV-2. Here, we report an in-flight transmission cluster of COVID-19 and describe the clinical characteristics of these patients. Methods: After a flight, laboratory-confirmed COVID-19 was reported in 12 patients. Ten patients were admitted to the designated hospital. Data were collected from 25th January to 28th February 2020. Clinical information was retrospectively collected. Results: All patients are passengers without flight attendants. The median age was 33 years, and 70% were females. None was admitted to intensive care unit, and no patients succumbed through 28th February. The median incubation period was 3.0 days and from illness onset to hospital admission was 2 days. The most common symptom was fever. Two patients were asymptomatic and negative for chest CT scan throughout the disease course. On admission, initial RT-PCR were positive in 9 patients, however initial chest CT were positive in only half patients. The median lung total severity score of chest CT was 6. Notably, Crazy-Paving pattern, pleural effusion, and ground-glass nodules were also seen. Conclusion: It is potential for COVID-19 transmission by airplane, but the symptoms are mild. Passengers and attendants must be protected during the flight.