Abstract: Objective To identify the clinical characteristics of obese patients with 2009 pandemic influenza A (H1NI) , providing the basis for development of clinical decision-making. Methods The clinical data on 42 obese patients with 2009 pandemic influenza A (H1NI) (the obesity group) and 72 non-obese patients with the same infection (the non-obesity group) being hospitalized from June 2009 to March 2010 were collected and analyzed retrospectively. Results Comparing with the non-obesity group, the obesity group demonstrated longer course of disease and duration of fever, more noticeable dyspnea, stethalgia and pulmonary rales, higher CRP (C-reactive protein) levels, more cases with abnormal myocardial enzymes, and higher incidence of combined pneumonia. The differences were significant (P0.05). The differences in the incidence of cough, sore throat, headache, and gastrointestinal symptoms, as well as the levels of routine blood tests and liver and renal functions, were insignificant between two groups (P0.05). Conclusion The clinical manifestations of 2009 pandemic influenza A (H1NI) are more severe in obese patients than in non-obese ones.