Abstract: Abstract: Objective To explore the relationship between rheumatoid arthritis (RA) and chronic periodontitis (CP) by observing the role of IL-18 in serum and gingival crevicular fluid (GCF) of patients with CP and RA. Methods 83 subjects were selected and divided into four groups: 16 healthy participants as the control group, 20 patients with CP, 21 patients with RA, and 26 patients with CP and RA. The serum and GCF levels of IL-18 were measured by enzyme-linked immunosorbent assay (ELISA), and clinical periodontal parameters including bleeding index (BI), probing depth(PD), and clinical attachment loss(CAL) were examined. Results The IL-18 levels in GCF of patients with CP and RA [(221.83±43.38) pg/ml] were significantly higher than those in the CP group [(198.00±37.72) pg/ml], RA group [(138.10±23.16) pg/ml] and the control group [(135.12±27.11) pg/ml] (P<0.05). Serum levels of IL-18 in the CP and RA group [(321.02±260.57) pg/ml], CP group [(220.60±228.37) pg/ml], RA group [(186.29±253.03) pg/ml] and HP group [(169.56±143.82) pg/ml] showed a decreasing trend. Only in CP and RA group, the serum levels of IL-18 were significantly higher than those in the control group (P<0.05). Conclusion IL-18 can be one of the biological foundations that correlates chronic periodontitis and rheumatoid arthritis.