Abstract: Objective To investigate the relationship between Chlamydia pneumoniae(Cpn)infection and the risk of lung cancer in Chinese Han people and to provide references for prevention of lung cancer.Methods A case-control study was conducted among 185 newly diagnosed lung cancer patients in three hospitals(the First Clinical Medical College of Fujian Medical University,the Affiliated Union Hospital of Fujian Medical University and Fuzhou General Hospital)and 190 non-cancer patients or physical examinees from the three hospitals during the same period as the controls betwecn July 2012 and January 2013.All the cases and controls had a face-to-face questionnaire survey and 5 ml blood sample collected for Cpn antibody IgG and IgA detection with Savyon^TM test.Results The positive rate the cases was 59.46%for IgG and 26.49%for IgA,which were all higher than those of the controls(34.21%and 6.84%)(P<0.05).After adjusting for sex,age,marital status,body mass index,education,and occupation,high titer of IgG(1:64-≥1:512)and IgA(1:32-1:64)increased the risk of lung cancer compared to the low titer of IgG(<1:64 and IgA<1:32),with the odds ratio(OR)of 2.44(95%confidence interval95%CI:1.56-3.81)and 3.79(95%CI:1.88-7.65),respectively.The Results also indicated that the IgG/IgA antibody and smoking,environment tobacco smoking(ETS),lung diseases and family history of lung cancer had synergistic effects on the incidence of lung cancer(P<0.05).Conclusion There is an association between Cpn infection and lung cancer.The IgG/IgA antibody and smoking,ETS,lung diseases and family history of lung cancer have synergistic effects on the incidence of lung cancer.