Background The occurrence and development of aortic aneurysm (AA) are associated with infection. Some researchers have detected the DNA of periodontal pathogens in AA samples in certain populations. However, it has not been done in Chinese population. The objective of this study was to evaluate the prevalence of periodontal pathogens in oral tissue samples and aneurysm samples of AA patients. Methods Eighty-nine subjects with AA and 59 subjects without AA were examined. Periodontal clinical parameters were evaluated. Unstimulated saliva and subgingival plaque samples were collected from all subjects. Twenty-six dissected AA samples were obtained. Evidence of eight periodontal pathogens including Porphyromonas gingivalis (Pg), Actinobacillus actinomycetemcomitans (Aa), Prevotella intermedia (Pi), Tannerella forsythensis (Tf), Treponema denticola (Td), Campylobacter rectus (Cr), Fusobacterium nucleatum (Fn), and Prevotella nigrescens (Pn) was ascertained in all samples by 16S rRNA-based polymerase chain reaction (PCR) assay. Results The periodontal indexes including plaque index (PLI), probing depth (PD), bleeding index (BI), and clinical attachment loss (CAL), of the six Ramfjord index teeth were significantly higher in the AA group than those in the control group (P <0.01). Eight periodontal pathogens in subgingival plaque samples were more frequently detected in the AA group than in control group. The difference in prevalence between the groups was significant for six (out of eight) periodontal pathogens assayed (Pg, Pi, Fn, Pn, Tf, and Td, P <0.01). Additionally, all eight periodontal pathogens were more frequently detected in saliva samples of the AA group than in those of the control group, again with six (out of eight) (Pg, Pi, Fn, Cr, Tf, and Td) displaying significant differences in prevalence between the two groups (P <0.01). Out of 26 aneurysm samples examined, Pg, Pi, Fn, Cr and Tf were detected in 6 (23.1%), 2 (7.7%), 3 (11.5%), 1 (3.8%), 2 (7.7%), respectively, and Aa, Pn, and Td were not detected in dissected aneurysm samples. Conclusion Results of this study suggested that periodontal infection is associated with the occurrence of AA.