Objective To investigate the effect of Porphyromonas gingivalis(P.gingivalis) fimbrillin(Fim) A on alveolar bone absorption resulting from P.gingivalis challenged periodontitis in mouse.Methods Mice were orally infected with the wild strains P.gingivalis ATCC33277,P.gingivalis KDP150 without fimA gene.Fifteen male,specific pathogen-free 3-week-old mice were divided into three groups: Control group,group infected with P.gingivalis ATCC33277,and group infected with P.gingivalis KDP150.After twenty two days,all animals were killed.The distance from the alveolar bone crest to the cemento-enamel junction was measured with Image-Pro software.Results Compared with control group,alveolar bone absorption was higher in the P.gingivalis ATCC33277 group(P 0.05),but no difference was observed between P.gingivalis KDP150 group and control group(P0.05).P.gingivalis ATCC33277 group was higher than P.gingivalis KDP150 group in alveolar bone absorption(P0.05).Conclusion P.gingivalis fimA is a potential virulence factor for alveolar bone absorption in the procedure of periodontitis.