Objective: Broad antiinflammatory effects following adenosine A_2A receptor stimulation have been demonstrated in acute inflammatory diseases, including arthritis. Polydeoxyribonucleotide (PDRN) activates the adenosine A_2A receptor. This study was undertaken to investigate the effects of PDRN in collagen‐induced arthritis (CIA) in mice.Methods: Arthritis was induced in DBA/1 mice by an intradermal injection of 100 μl of bovine type II collagen in Freund's complete adjuvant. Mice were immunized a second time 21 days later. Control animals received 100 μl of a saline solution. Animals with CIA were randomized to receive one of the following: vehicle (1 ml/kg); PDRN (8 mg/kg intraperitoneally daily); 3,7‐dimethyl‐propargylxanthine (DMPX), a specific adenosine A_2A receptor antagonist (0.1 mg/kg intraperitoneally daily); or PDRN plus DMPX. The treatment was initiated immediately after the second immunization and continued to day 45. Clinical evaluation of arthritis was performed throughout the study. On day 45, the animals were killed and the severity of arthritis was evaluated histologically. Cartilage expression and circulating levels of high mobility group box chromosomal protein 1 (HMGB‐1), tumor necrosis factor α (TNFα), interleukin‐6 (IL‐6), and IL‐10 were investigated. Inflammatory cytokine production was also evaluated in stimulated human chondrocytes treated with PDRN.Results: PDRN treatment significantly ameliorated clinical signs of arthritis, improved histologic damage, reduced the cartilage expression and circulating levels of HMGB‐1, TNFα, and IL‐6, and enhanced IL‐10 expression. The concomitant administration of DMPX and PDRN ablated the PDRN‐induced protective effect in experimental arthritis. PDRN also reduced cytokine production from stimulated human chondrocytes.Conclusion: Our findings indicate that PDRN may represent a new alternative for the treatment of arthritis.