To investigate the status and influencing factors of illness uncertainty among patients with coronavirus disease 2019 (COVID-19) in the mobile cabin hospital. A cross-sectional study. 114 patients with COVID-19 admitted to a mobile cabin hospital in Wuhan, Hubei Province, in February 2020 were enrolled by a convenience sampling method. The Chinese version of the Mishel Illness Uncertainty Scale (MUIS) was used to assess patients' degree of illness uncertainty, and multiple regression analysis was used to explore the influencing factors. The average total score of MUIS (Chinese version) was 52.22 ± 12.51, indicating a moderate level of illness uncertainty. The dimension unpredictability turned out to have the highest mean score: 2.88 ± 0.90. The multiple stepwise regression analysis showed that female (t = 2.462, p = .015), monthly family income not less than RMB 10,000 (t = -2.095, p = .039), and disease duration of 28 days or more (t = 2.249, p = .027) were independent influencing factors of illness uncertainty. Patients with COVID-19 are at a moderate level of illness uncertainty. Medical staffs should pay more attention to female patients, patients with lower monthly family income, patients with the prolonged disease, and take targeted interventions to help them reduce illness uncertainty. Facing the brand new and unknown infectious disease, patients confirmed of COVID-19 suffer from immense physical and psychological stress, where illness uncertainty is a major stressor that troubles patients. The present study surveys illness uncertainty among patients with COVID-19 in the mobile cabin hospital with results revealing a moderate level. Study results will benefit nurses in any setting where care for patients with COVID-19 is provided, public policymakers and future researchers. © 2021 The Authors. Nursing Open published by John Wiley & Sons Ltd.