Abstract: Objective To summarize the clinical characteristics of severe human adenovirus type 55 pneumonia. Methods Clinical data about 6 patients with severe human adenovirus type 55 pneumonia admitted to our department from April 2013 to May 2013 were retrospectively analyzed. Results The 6 patients were adult males aged 25-40 years from Baoding, Hebei Province. Their clinical symptoms included fever, cough, expectoration, and dyspnea with mental symptoms appeared in some of them. Their serum CRP and IL6 level and neutrophils were higher while their white blood cells were lower, normal or elevated. Laboratory test demonstrated that their serum alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase levels were higher while their serum albumin level was lower. Chest CT showed large pulmonary consolidation, cavities, mediastinal emphysema, and subcutaneous pneumatosis, etc. Of the 6 patients, 4 were discharged and 2 died after anti-infection and glucocorticoid treatment, and endotracheal intubation-assisted ventilation, etc. Conclusion Severe human adenovirus type 55 pneumonia in adults progresses rapidly with a long course and a high mortality, and should be treated as soon as possible.