Objective To assess the relationship between the Chlamydia pneumonia(CPn)infection and coronary heart disease(CHD).Methods Blood samples from 200 CHD patients and 100 heathy controls were col-lected,and Cpn IgM and Cpn IgG were tested by ELISA.Results The Cpn IgM were found in 113 cases (56.5%) and in 24 controls(24.0%).The Cpn IgG positive cases were in 145(72.5%) patients and in 43 controls (43.0%).The positive rate of Cpn IgM and Cpn IgG in CHD group Was higher than that in control group(P<0.05).Conclusion:CPn positive rate is higher in CHD group than that in control group.Cpn is closely related to the pathogenesis of CHD.