Objective: To detect the expression of matrix metalloproteinase-3 (MMP-3) in serum and gingival crevicular fluid in patients with rheumatoid arthritis (RA) and its correlation with chronic periodontitis (CP). Methods: From March 2017 to July 2018, 26 patients with RA and CP [CP+RA group, (54.9±6.5) years old, 4 males and 22 females], 22 patients with RA only [RA group, (49.6±11.7) years old,5 males and 17 females] in the Department of Rheumatology and Immunology, Shengjing Hospital Affiliated to China Medical University, 22 patients with simple CP in the Department of Stomatology, Shengjing Hospital Affiliated to China Medical University [CP group, (51.4±12.5) years old, 8 males and 14 females] and 18 generally healthy controls in Physical Examination Center of Shengjing Hospital Affiliated to China Medical University [group H, (49.4±9.1) years old, 8 males and 10 females] were recruited. There were no significant differences in age and sex ratio amongst 4 groups. Patient's general status, probing depth (PD) , clinical attachment loss (CAL), sulcus bleeding index (SBI), simplified calculus index (CI-S) and simplified debris index (DI-S) were recorded in 4 groups. Samples of serum and gingival crevicular fluid were collected from patients of each group, and the expression levels of MMP-3 in serum and gingival crevicular fluid samples were detected by using enzyme-linked immunosorbent assay. Erythrocyte sedimentation rate, rheumatoid factor, anti-cyclic citrulline peptide antibody and C-reactive protein were detected in the serum of subjects in RA group and CP+RA group. Correlation analysis was conducted between MMP-3 expression level and periodontal indices amongst 4 groups. The results were statistically analyzed using the SPSS 20.0 software package. Results: The indices of CAL [(4.12±1.13) mm], SBI (2.58±0.64) and DI-S (2.65±0.69) in CP+RA group were significantly higher than indices of CAL [(3.00±0.00) mm], SBI (2.59±1.05) and DI-S, (2.36±0.49) in CP group (P<0.05); The expression levels of MMP-3 in serum samples of CP+RA group [(1 1645.6±6 903.4) μg/L] and CP group [(9 337.0±6 719.0) μg/L] were significantly higher than that of RA group [(2 389.9±1 320.3) μg/L] and H group [(1 493.5±292.1) μg/L] (P<0.05). The expression level of MMP-3 in gingival crevicular fluid samples of CP+RA group [(164.4±45.3) μg/L] was significantly higher than that of CP group [(84.6±92.5) μg/L], RA group [(49.0±18.1) μg/L] and H group [(20.4±6.3) μg/L] (P<0.05), respectively. The erythrocyte sedimentation rate, rheumatoid factor and anti-cyclic cirullinated peptide antibodies levels in the CP+RA group were significantly higher than those in the RA group (P<0.05). The expression level of MMP-3 in serum is positively correlated with PD (r=0.45, P=0.04) and the expression level of MMP-3 in gingival crevicular fluid is positively correlated with CAL (r=0.58, P<0.01). Conclusions: The levels of MMP-3 in serum and gingival crevicular fluid of patients with RA and CP were significantly increased. MMP-3 may be associated with the development of CP and RA.