Aim To investigate the effect of C.pneumoniae infection on the expression of peroxisome proliferator-activated receptor γ(PPARγ),nuclear factor-κB(NF-κB) and activated protein-1(AP-1) in aortic endothelial cell in hyperlipidemia mice. Methods Forty-eight,8-week-old female C57BL/6J mice were divided into 4 groups: control group,infected group,atherogenic diet group and infected atherogenic diet group(each twelve).14 weeks later,the expression of PPARγ,P50(subunit of NF-κB) and cFos(subunit of AP-1) was determined by indirect immunofluorescence in the aortic endothelial cell.Slides of aortic sinus were prepared by cryosection,and stained with Sudan Ⅳ for examination of atherosclerotic plaque.The score of atherosclerotic plaque was determined by microscopy. Results The score of atherosclerotic plaque in infected group was not increased,while it was significant higher in atherogenic diet group and infected atherogenic diet group(p<0.01),still the score in infected atherogenic diet group was higher than in atherogenic diet group(p<0.01).The expression of PPARγ,NF-κB and AP-1 in endothelial cell in aortic sinus was upregulated in infected group,atherogenic diet group and infected atherogenic diet group,in comparison with that in control group(p<0.05).There was no significant difference among infected group,atherogenic diet group and infected atherogenic diet group. Conclusion The inflammatory process was already initiated in the aortic endothelial cell in C57BL/6J mice at the early stage of Chlamydia pneumoniae infection and hyperlipidemia.Chlamydia pneumoniae infection alone would not accelerate the process of atherosclerosis.But Chlamydia pneumoniae infection could accelerate the process of atherosclerosis.