Objective : To investigate the expression and clinical significance of tryptophan⁃2 ,3 ⁃dioxygenase⁃2 (TDO2) in peripheral blood mononuclear cells ( PBMC) and synovial tissue of patients with rheumatoid arthritis (RA) . Methods : A total of 40 RA patients were selected as the RA group , and 36 healthy subjects were selected as the normal control group during the same period. In RA group and control group PBMC , TDO2 expression was detected by flow cytometry. Immunofluorescence was applied to observe TDO2 expression in synovial tissue of RA groups and control group. The correlation was analyzed between TDO2 expression in PBMC and their inflammatory indicators of RA groups. Results : Compared with control group , TDO2 expression in RA group PBMC and synovial tissue significantly increased (P < 0. 001) ; TDO2 expression in RA group PBMC was positively correlated with erythrocyte sedimentation rate (ESR) ( r = 0. 405 , P = 0. 045) . Conclusion The expression of TDO2 is up⁃regulated in RA patients PBMC and synovial tissue , and positively correlates with inflammatory indicators ESR , suggesting that TDO2 may participate in RA disease progression.