Objective To explore the etiologies of fever of unknown origin(FUO)and methods for confirming di-agnosis in patients at a hospital,and provide reference for clinical diagnosis and treatment of FUO.Methods Pa-tients with FUO admitted to a hospital between January 2008 and July 2014 were performed clinical diagnosis with methods of serology,bacteriology,molecular biology,bone marrow aspiration,tissue biopsy,and diagnostic thera-py,the etiologies and final diagnosis of 224 patients were analyzed retrospectively.Results Of 224 FUO cases,189 (84.38%)eventually got confirmed diagnosis,35 (15.62%)were not confirmed.The percentage of infectious dis-eases,connective tissue diseases,malignant tumor,and other diseases were 50.45%,18.75%,9.82%,and 5.36%respectively.Among infectious diseases,the major pathogens were bacteria,followed by virus.The major connec-tive tissue diseases were systemic lupus erythematosus and polyarteritis nodosa;the main malignant tumor was he-matological tumor,lymphoma was the main form.Among 189 patients with confirmed diagnosis,30.16% and 24.34% were performed pathogenic and pathologic detection respectively,and 20.11% were performed the other (compre-hensive)methods.Conclusion Infectious diseases,connective tissue diseases,and tumor are major etiologies of FUO.