Objective: To study the relationship between Chlamydia pneumoniae (C. Pneumoniae) infection and asthma exacerbation. Methods: A prospective study of C. Pneumoniae infection was conducted in 75 patients with asthma and 63 patients with respiratory tract infection, and 100 blood donors served as controls.The presence of infection was convinced by the polymerase chain reaction and direct immunofluorescence assay for C. Pneumoniae DNA from throat swab specimens and micro-immunofluorescence testing for C. Pneumoniae-specific IgG, IgM and IgA antibodies. Results: Prevalence of specific IgG in asthma patients (81.3%) was higher than that of the blood donors (68. 0%, P＜0. 05) and was not significantly different from respiratory tract infection patients (68. 0%, P＞0. 05). The acute C. Pneumoniae infection rate of symptomatic asthma patients (59.4%) was markedly higher than that of respiratory tract infection patients (34.9%, P＜0. 05). The average titer of C. Pneumoniae IgG instead of IgA in asthma patients (48. 38±6. 94)was significantly higher than respiratory tract infection patients (24. 70±8. 77, P＜0. 05). Other pathogens were identified in 12 of 21 (57. 1%) asthma patients with C. Pneumoniae. The symptoms of 7 asthma patients with C. Pneumoniae infection were improved through antibiotic treatment. Conclusion: The findings suggest a possible role of C. Pneumoniae infection in asthma.