Objective To investigate the expression of high mobility group protein B1 (HMGB1) in rheumatoid arthritis. Methods Forty-nine patients with rheumatoid arthritis who underwent joint replacement or synovectomy in the First Hospital of Jilin University from May 2017 to May 2018 were selected as the subjects. In addition, 30 patients with osteoarthritis who underwent surgery in the same hospital during the same period were selected as the control group. The peripheral venous blood was collected in the morning of the 3rd day after admission and the serum was separated. The serum content of HMGB1 was determined by enzyme-linked immunosorbent assay. And the expression of HMGB1 in the diseased synovial tissues was detected by immunohistochemical SP method. Results The serum HMGB1 level of the study group was higher than that of the control group (P < 0.05). The positive expression rate of HMGB1 in the study group was higher than that in the control group (P < 0.05). The score of immunohistochemical SP staining in the study group was higher than that in the control group (P < 0.05). Conclusions The high expression of HMGB1 in rheumatoid arthritis may play an important role in the pathogenesis of tissue damage in rheumatoid arthritis, and HMGB1 may be used as an auxiliary index in the diagnosis and treatment of rheumatoid arthritis.