Background The incidence, severity, and outcomes of AKI in COVID-19 varied in different reports. In patients critically ill with COVID-19, the clinicopathologic characteristics of AKI have not been described in detail. Methods This is a retrospective cohort study of 81 patients critically ill with COVID-19 in an intensive care unit. The incidence, etiologies, and outcomes of AKI were analyzed. Pathologic studies were performed in kidney tissues from ten deceased patients with AKI. Results A total of 41 (50.6%) patients experienced AKI in this study. The median time from illness to AKI was 21.0 (IQR, 9.5-26.0) days. The proportion of Kidney Disease Improving Global Outcomes (KDIGO) stage 1, stage 2, and stage 3 AKI were 26.8%, 31.7%, and 41.5%, respectively. The leading causes of AKI included septic shock (25 of 41, 61.0%), volume insufficiency (eight of 41, 19.5%), and adverse drug effects (five of 41, 12.2%). The risk factors for AKI included age (per 10 years) (HR, 1.83; 95% CI, 1.24 to 2.69; P=0.002) and serum IL-6 level (HR, 1.83; 95% CI, 1.23 to 2.73; P=0.003). KDIGO stage 3 AKI predicted death. Other potential risk factors for death included male sex, elevated D-dimer, serum IL-6 level, and higher Sequential Organ Failure Assessment score. The predominant pathologic finding was acute tubular injury. Nucleic acid tests and immunohistochemistry failed to detect the virus in kidney tissues. Conclusions AKI was a common and multifactorial complication in patients critically ill with COVID-19 at the late stage of the disease course. The predominant pathologic finding was acute tubular injury. Older age and higher serum IL-6 level were risk factors of AKI, and KDIGO stage 3 AKI independently predicted death.