Background: To identify the differences of epidemiology, clinical features, laboratory findings and clinical outcomes of severe pneumonia children under 5 years old among with and without ADV infection.Methods: A retrospective cohort study was conducted in three pediatric hospitals in Guangzhou, China. All children under the age of 5 for sever pneumonia and admitting ICU during 1 January 2009 and 31 December 2019. Demographics, complications, the first routine laboratory findings, therapeutic records and clinical outcome were collected from electronic medical records. We compared characteristics of children with and without ADV infection.Results: ADV were detected in 75 (4.7%) of 1595 severe pneumonia children. Cases with ADV infection were more likely to be male, older than one year old, combined other microbial infections, but less likely to have mixed virus infections and combined with cardiovascular disease, and had more abnormal laboratory results than cases without ADV infection. Antiviral therapy was rarely used in children with severe pneumonia, but antibiotic therapy was commonly used in severe pneumonia children, especially cases with ADV infection (91.9%). Children infected with ADV were also hospitalized longer and had a higher mortality within 30 days of hospitalization.Conclusions: Severe pneumonia children under 5 years old with ADV infection had more abnormal laboratory findings and more severe clinical outcomes than cases without ADV infection. More attention should be focused on the harm caused by ADV infection.