Background: Coronavirus disease 2019 (COVID-19) is a global outbreak disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Cytomegalovirus (CMV) infection can occur in critical COVID-19 patients and is associated with adverse clinical outcomes. Objective: The aim of this study was to explore the clinical characteristics and outcome of CMV infection in critical COVID-19 patients. Design: This was a retrospective cohort study. Methods: From May to September 2021, SARS-CoV-2 reverse transcription polymerase chain reaction (RT–PCR)-confirmed COVID-19 patients with intensive care unit (ICU) admission were enrolled. CMV infection was confirmed by PCR. Baseline characteristics, critical illness data and clinical outcomes were recorded and analyzed. Results: Seventy-two RT–PCR-confirmed COVID-19 patients with ICU admission were included during the study period and 48 (66.7%) patients required mechanical ventilation (MV). Overall, in-hospital mortality was 19.4%. Twenty-one (29.2%) patients developed CMV infection. Patients with CMV infection had a higher likelihood of diabetes, higher lactate dehydrogenase and lactate levels, and higher proportions of MV, anticoagulant, and steroid use. Patients with CMV infection were associated with longer duration of SARS-CoV-2 shedding, longer ICU and hospital stay, and fewer ventilator-free days. The independent risk factor for development of CMV infection was a higher accumulative steroid dose. Conclusion: CMV infection adversely impacted the outcomes of critical COVID-19 patients, resulting in longer ICU stays, longer mechanical ventilation uses and prolonged shedding of SARS-CoV-2.