Background: Coronavirus disease 2019 (COVID-19) has caused more than 2 million deaths worldwide. Viral sepsis has been proposed as a description for severe COVID-19, and numerous therapies have been on trials based upon this hypothesis. However, whether the clinical characteristics of severe COVID-19 are similar to those of bacterial sepsis has not been elucidated. Methods: We retrospectively compared the clinical data of non-surviving COVID-19 patients who were admitted to a 30-bed intensive care unit (ICU) in Wuhan Infectious Diseases Hospital (Wuhan, China) from 22 January 2020, to 28 February 2020, with those of non-surviving patients with bacterial sepsis who were admitted to the ICU in Zhongshan Hospital, Fudan University (Shanghai, China) from 3 July 2018, to 30 June 2020. Results: A total of 53 COVID-19 patients and 26 septic patients were included in the analysis. The mean ages were 65.6 [standard deviation (SD): 11.1] and 70.4 (SD: 14.3) years in the COVID-19 cohort and sepsis cohort, respectively. The proportion of participants with hypertension was higher in non-survivors with COVID-19 than in non-survivors with sepsis (41.5% vs. 15.4%, P=0.020). The Sequential Organ Failure Assessment (SOFA) score of non-survivors with COVID-19 was lower than that of non-survivors with sepsis at ICU admission {4.0 [interquartile range (IQR): 3.0-6.0] vs. 7.5 [IQR: 5.8-11.0], P<0.001}. The clinical parameters at ICU admission assessed with principal component analysis and hierarchical cluster analysis showed that COVID-19 patients were distinct from bacterial septic patients. Compared with non-survivors with sepsis, non-survivors with COVID-19 had a higher neutrophil/lymphocyte ratio, total protein, globulin, lactate dehydrogenase (LDH), and D-dimer; a lower eosinophil count, procalcitonin, interleukin-6 (IL-6), total bilirubin, direct bilirubin, myohemoglobin, albumin/globulin ratio, activated partial thromboplastin time (APTT), prothrombin time (PT), and international normalization ratio (INR) at ICU admission. In addition, the levels of total protein, globulin, LDH, D-dimer, and IL-6 were significantly different between the two groups during the ICU stay. Conclusions: Patients with critical COVID-19 have a phenotype distinct from that of patients with bacterial sepsis. Therefore, caution should be used when applying the previous experience of bacterial sepsis to patients with severe COVID-19.