Abstract： Objective： To observe the therapeutic effect of Modified Yutong Pills on ankylosing spondylitis and its influence on serum Janus kinase/signal transducer and activator of transcription (JAK/ STAT) signaling pathway. Methods：A total of 92 patients with ankylosing spondylitis were randomly divided into the control group and the observation group， with 46 cases in each group. The control group was treated with Methotrexate，and the observation group was supplemented with modified Yutong Pills based on the treatment of the control group. The course of treatment was 8 weeks. The scores of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)，Spondyloarthritis Research Consortium Canada (SPARCC) and traditional Chinese medicine (TCM) syndromes， and the levels of serum inflammatory factors， including tumor necrosis factor-α (TNF-α)，interleukin-1β (IL-1β)，interleukin-6 (IL-6) and macrophage migration inhibitory factor (MIF)，immunoglobulin，including immunoglobulin G1 (IgG1)，immunoglobulin G2 (IgG2)， immunoglobulin A (IgA) and immunoglobulin M (IgM)， pain mediators， including endothelin- 1 (ET- 1)， prostaglandin E2(PGE2)， substance P (SP) and cyclooxygenase- 2 (COX- 2)， and JAK/STAT signaling pathways，including Janus kinase (JAK)，phosphorylated JAK (p-JAK)，signal transducer and activator of transcription 3 (STAT3) and phosphorylated STAT3 (p- STAT3)， were compared between the two groups before and after treatment， and the clinical effects in the two groups were compared. Results： After treatment and follow- up for 3， 6 and 12 months， the total effective rate was respectively 97.7% ， 72.7%，52.3% and 38.6% in the observation group，higher than that of 83.3%，40.5%，16.7% and 4.8% in the control group (P＜0.05). After treatment and follow- up for 3， 6 and 12 months， the scores of BASDAI， SPARCC and TCM syndromes were decreased in the observation group (P＜0.05)， and after treatment and follow-up for 3 months，the scores of BASDAI and SPARCC were decreased in the control group (P＜0.05)；after treatment and follow-up for 3，6 and 12 months the scores in the observation group were lower than those in the control group at the same period (P＜0.05). After treatment， the levels of TNF-α，IL-1β，IL-6 and MIF in the observation group were decreased (P＜0.05)，and the TNF-α level in the control group was decreased (P＜0.05)， and the levels of TNF- α， IL- 1β， IL- 6 and MIF in the observation group were lower than those in the control group (P＜0.05). After treatment， the levels of IgG1，IgG2，IgA and IgM in the observation group were increased (P＜0.05)，and those in the observation group were higher than those in the control group (P＜0.05). After treatment，the levels of ET-1，COX-2 and PGE2 in the two groups were decreased (P＜0.05)， and the SP level in the observation group was decreased (P＜0.05)；the levels of ET-1，COX-2，SP and PGE2 in the observation group were lower than those in control group (P＜0.05). After treatment，the JAK and STAT3 levels in the observation group were increased (P＜0.05)，and the p-JAK and p-STAT3 levels were decreased (P＜0.05)，and the p-JAK level in the control group was decreased (P＜0.05)； the JAK and STAT3 levels in the observation group were higher than those in the control group (P＜0.05)，and the p-JAK and p-STAT3 levels were lower than those in the control group (P＜0.05). There was no significant difference in the incidence of adverse reactions between the two groups (P＞0.05). Conclusion： Modified Yutong Pills can effectively relieve the clinical symptoms of patients with ankylosing spondylitis，and its mechanism may be related to the regulation of serum JAK/STAT signaling pathway.