Abstract: Objective To systematically evaluate the relationship of Chlamydia pneumoniae(Cpn) infection with lung cancer and to provide a scientific basis for etiology research and clinical diagnosis and treatment of lung cancer.Methods Medline,Sinomed,China National Knowledge Infrastructure,VIPdisc,WanFang Data and other databases were searched for the case-control studies on the association of Cpn infection with lung cancer.Meanwhile,Google Scholar was used to handsearch for addendum to the databases based on the references of the articles retrieved.Stata 12.0 software was applied in meta-analysis.Results Totally 12 eligible studies(9 English articles and 3 Chinese articles) were included,involving 2 557 lung cancer cases and 2 756 controls.The pooled odds ratios(ORs) for Cpn antibody IgA-positive and IgG-positive were 2.025(95% confidence interval 95%CI:1.376-2.982) and 1.774(95%CI:1.251-2.516).The pooled ORs for Cpn antibody IgA-positive and IgG-positive were 2.372(95%CI:1.463-3.847)and 1.908(95%CI:1.112-3.275)among smokers.Cpn infection was identified as a risk factor for lung cancer for the subjects with Cpn antibody IgA of ≥16 cutoff value(OR=1.180,95%CI:1.029-1.353),IgA of ≥64(OR=1.836;95%CI:1.098-3.068),and IgG of ≥16(OR=1.608,95%CI:1.022-2.531)Conclusion Cpn infection is associated with lung cancer,particularly among smokers.