〔Abstract〕 Objective To explore the effect of body mass index(BMI) on sarcopenia in patients with rheumatoid arthritis(RA). Methods 468 RA patients and 223 age and gender-matched healthy controls were selected. The BMI, skeletal muscle mass, skeletal muscle mass of the extremities, body fat percentage and protein content were measured using a bioelectrical impedance Inbody720 body composition analyzer.BMI was calculated according to weight(kg)/height(m)2and four groups were divided according to BMI,weight loss(BMI<18.5),normal(18.5≤BMI<24),overweight(24≤BMI<28)and obesity(BMI≥28). Appendicular skeletal muscle index(ASMI) was calculated according to limb skeletal muscle mass(kg)/height(m)2as a criterion for sarcopenia. Results ① The percentage of weight loss in the RA group was higher than that in the control group(12.6% vs 4.5%, χ2=11.086, P=0.001). ② The incidence of sarcopenia in the RA group was 51.1%, which was higher than that in the control group(24.2%)(χ2=44.593, P<0.000 1).③ The BMI, skeletal muscle mass, limb skeletal muscle mass and protein content of the RA group were lower than those of the control group, while the percentage of body fat was higher than that of the control group(P<0.05). ④ There was a difference in the incidence of sarcopenia between different BMI groups in the RA group(χ2=82.437, P<0.000 1). The incidence of sarcopenia in the BMI weight loss group and the normal group was higher than that in the overweight or obesity group( P<0. 000 1). The incidence of sarcopenia was the highest in the BMI weight loss group,and there was no significant difference in the incidence of sarcopenia between the overweight and obesity groups( P>0. 05).(5) The age of RA patients with sarcopenia was higher than that of RA patients without sarcopenia,and the BMI of RA patients with sarcopenia was lower than that of RA patients without sarcopenia( P<0. 05).(6) There was a statistically significant difference in the BMI between the RA with sarcopenia and RA without sarcopenia( χ2= 82. 437,P<0. 000 1). The BMI weight loss and normal percentage in the RA with sarcopenia were higher than those in RA without sarcopenia; and the BMI overweight and obesity percentage in the RA with sarcopenia were less than those in RA without sarcopenia( P<0. 01).(7) Multivariate logistic regression analysis showed that referring to the RA patients in the normal BMI group,the risk of sarcopenia in the weight loss group was increased,while the risk of sarcopenia in the overweight or obesity group was reduced; in addition,protein content was a protective factor for sarcopenia in RA patients,age and body fat percentage were risk factors for sarcopenia in patients with RA. Conclusion The incidence of sarcopenia is higher in patients with RA. BMI is a protective factor for the incidence of sarcopenia in patients with RA.