Objective:To investigate the clinical efficacy of Tofacitinib combined with leflunomide in the treatment of rheumatoid arthritis (RA) and its effects on Janus Kinase (JAK)/signal transduction and activator of transcription (STAT) signaling pathway-related proteins and Matrix metalloproteinase levels in serum of patients with RA.Methods:This was a prospective case-control study. A total of 80 patients with RA in our hospital from March 2020 to September 2021 were included into the study. They were divided into observation group and control group by random number table method, with 40 cases in each group. The patients in observation group were treated with Tofacitinib combined with leflunomide, while the patients in control group were treated with leflunomide alone. After 12 weeks of continuous treatment, the curative effect of the two groups was observed. Typical clinical manifestation [including Visual analogue scale (VAS) score of joint pain, number of tenderness joints, number of swollen joints, time of morning stiffness], disease activity score uses 28 joint counts (DAS28) scores, the MOS item short from health survey (SF-36) total scores and serum JAK3, STAT3, interleukin (IL)-6, IL-17 and matrix metalloproteinase (MMPs) levels were compared between the two groups before and after treatment. The adverse effects of the two groups were also analyzed. Chi-square test, paired sample t test, independent sample t test and Fisher exact probability method were used for statistical analysis. Results:After 4, 8 and 12 weeks of treatment, the american college of rheumatology (ACR)20 compliance rates in the observation group were 37.5%(15/40), 62.5%(25/40) and 80.0%(32/40), respectively, which were significantly higher than those in the control group at the same period [17.5%(7/40), 37.5%(15/40), 57.5%(23/40); χ2=4.01, P=0.045; χ2=5.00, P=0.025; χ2=4.71, P=0.030]. After 8 and 12 weeks of treatment, the ACR50 compliance rates in the observation group were [35.0%(14/40) and 47.5%(19/40), respectively, which were significantly higher than those in the control group at the same period 15.0%(6/40) and 20.0%(8/40), χ2=4.27, P=0.039; χ2=6.76, P=0.009]. After treatment, the joint pain VAS score, number of tenderness joints, number of swollen joints, DAS28 scores and SF-36 total scores in the observation group were lower than those in the control group( t=5.55, P<0.001; t=9.98, P<0.001; t=11.77, P<0.001; t=4.50, P<0.001; t=5.28, P<0.001), and time of morning stiffness was shorter than that in the control group ( t=4.76, P<0.001). After treatment, The serum levels of JAK3, STAT3, IL-6, IL-17, MMP-3, MMP-9 and MMP-13 in the obser vation group were (2 354±476) pg/ml, (1.04±0.17) ng/ml, (12.4±2.8) pg/ml, (30±5) pg/mL, (65±14) μg/L, (76±12) μg/L, (11.5±1.8) μg/L, which were lower than those in control group [(2 715±584) pg/ml (1.22±0.29) ng/mL, (16.8±3.6) pg/ml, (40±7) pg/ml, (98±15) μg/L, (123±20) μg/L, (14.9±2.8) μg/L, t=3.03, P<0.05; t=3.39, P<0.05; t=6.10, P<0.05; t=7.35, P<0.05; t=10.17, P<0.05; t=12.74, P<0.05; t=6.46, P<0.05]. The adverse reaction rate of the observation group [35.0%(14/40)] had no statistically significant difference compared with that in the control group [27.5%(11/40)]( χ2=0.52, P=0.469). Conclusion:The overall effect of Tofacitinib com bined with leflunomide in the treatment of RA is satisfactory and it is a safe and effective way to improve the clinical manifestation, disease activity and quality of life of patients with RA. The effect may be related to the significant down-regulation of the expression levels of Serum JAK/STAT signaling pathway-related Proteins and MMPs.