Objective To investigate the relationship between the expression of sero-activin A and rheumatoid arthritis.Methods Seventy-one RA patients admitted to The Affiliated Hospital of Southwest Medical University from January 2020 to August 2020 were enrolled in case group. Forty subjects were enrolled to healthy control group in the same period. ELISA was used to detect the expression of ACT-A in both group. According to upper and lower quartile of ACT-A， RA patients were divided into low level group (<27.54ng/m)， medium level group(27.54～39.14ng/ml) and high level group(>39.14ng/ml). Clinical data and laboratory indicators were compared in the 3 groups. The relationship between ACT-A and clinical data/ laboratory indicators were analyzed.Results Sero-activin A was significant higher in RA patients compared to health controls (P<0.05)， tenderness joint count (TJC)， disease active score 28 (DAS28) is higher in high level group compared to low level group and medium level group， swollen joint count (SJC) in high level group is higher than low level group. Pearson correlation analysis showed that serum ACT-A was related to TJC， SJC and DAS28， but there was no significant relationship with age， disease duration， rematoid factor(RF)， anti-CCP antibody， anti-MCV antibody， C-reactive protein， erythrocyte sedimentation rate， IgA， IgM， IgG， complement C3， complement C4.Conclusion Serum ACT-A is significant higher in RA patients which is positively correlate to TJC， SJC and DAS28， and it may be a reference index for RA disease activity.