Objective: To analyze the infection rates of 9 commonly seen pathogens [Parainfluenza virus (PIV), Influenza virus A (INFA), Influenza virus B (INFB), Respiratory syncytial virus (RSV), Adenovirus (ADV), Legionella pneumophlia serogroup 1 (Lp1), Mycoplasma pneumoniae (MP), Coxiella burnetii (Cb)], Chlamydophila pneumonia (CP)] among patients with acute respiratory tract infection. Method: A total of 2 241 samples were collected from inpatients at the Qingpu Branch of Zhongshan Hospital, Fudan University during 2015-2016. IgM antibodies of the nine pathogens in inpatients with respiratory infection were detected by indirect immunofluorescence method. The clinical epidemiological characteristics by age group, pathogen type and seasons were analyzed. Results: Of all the 2 241 patients, 447 cases were shown to be positive for the 9 pathogens, with a total positive rate of 19.95%. There were 345 cases (77.18%) with single pathogen infection, and 102 cases (22.82%) with mixed infection. Of the 9 pathogens, constituent ratio of Mp infection was the highest [41.16% (184 cases)], followed by Lp1[121cases (27.07%)]. For seasons by spring, summer, autumn, winter, the positive rates were 16.42%, 18.08%, 20.72%, 23.94%, respectively. In different age groups, the positive rate were 21.84% (<12 years), 16.25% (12-59 years） and 21.08% (≥60 years), respectively. Conclusions: MP is the major pathogen in patients with respiratory tract infection for all 4 seasons. Detection rates of MP in patients with age <12 and 12-59 are the highest,and so is the detection rate of Lp1 during the summer.