ObjectiveTo evaluate the causes and clinical features of 245 fever of unknown origin(FUO) cases.MethodsClinical data of 245 hospitalized FUO patients from January,2009 to April, 2011 in a hospital were analyzed retrospectively.ResultsOf 245 patients with FUO, 220 cases (89.80%) were diagnosed definitely，25 cases (10.20%) were still not diagnosed definitely when they discharged from hospital. The overall etiology distribution were as follows: 158 (64.49%) were infectiou diseases, 63.92%(101/158) of which were caused by bacteria/fungi， 23.42% (37/158) were tuberculosis; 33(13.47%) were connective tissue disease(CTD), 60.16%(20/33) of which were adultonset Still’s disease; 22 (8.98%) were tumor, 59.09%(13/22) of which were lymphoma; 7（2.86%） were other diseases.ConclusionThe main causes in FUO are infectious diseases, bacteria/fungi infection is the most common cause; In addition, the percentage of the CTD and tumor are also relatively high. Most FUO cases can be diagnosed definitely through careful physical examination, clinical analysis, and necessary laboratory test.