BACKGROUND The association of periodontitis (PD) with the prevalence of rheumatoid arthritis (RA) remains controversial. Therefore, the aim of this study was to evaluate their correlation and investigate the effects of non-surgical periodontal treatment on RA. MATERIAL AND METHODS A total of 64 patients were enrolled in this study and divided into 4 groups: 18 PD patients (PD+RA-), 18 RA patients (PD-RA+), 18 RA with PD patients (PD+RA+), and 10 healthy controls (PD-RA-). Periodontal and rheumatologic parameters were examined at baseline and 1 month following non-surgical periodontal treatment. RESULTS Our results showed that RA patients had similar periodontal status. However, patients in the PD+RA+ group had significantly higher levels of rheumatologic parameters such as C-reactive protein (CRP), anti-cyclic citrulline peptide antibody (ACPA), erythrocyte sedimentation rate (ESR), and Disease Activity Score 28 (DAS28) than those in the PD-RA+ group. In addition, non-surgical periodontal treatment was efficacious in improving rheumatologic parameters of patients in the PD+RA+ group. CONCLUSIONS The presence of PD might contribute to the progression of RA, while RA might have little effect on accelerating the development of PD. In addition, RA patients with PD receiving non-surgical periodontal treatment resulted in noteworthy improvement in the clinical outcome for RA.