Abstract: OBJECTIVE To investigate the effect of Yiceng on the synovial fibrosis in KOA rats based on HMGB1. METHODS SPFSD 30 rats were randomly devided into normal group， model group and Yiceng group equally. The KOA model by injected sodium iodoacetate into The knee. After modeling，The Yiceng group was applied Yiceng for 28 days. After the final administration， blood was collected from the abdominal aorta and synovial tissues of each group wereextracted， Synovitis was observed by HE staining; Detecting proinflammatory cytokines: IL-1β， IL- 6， TNF-α and Inflammatory cytokines: IL-4， IL-10， TGF-β by ELISA; then detected HMGB1， α-SMA， TIMP1， CollagenⅠand Collagen Ⅲ protein and gene expression in synovium by Western Blot and qPCR. RESULTS HE staining showed that inflammatory cell infiltration in the yiceng group was significantly reduced compared with the model group， and the arrangement was relatively regular.The contents of IL-1β，IL-6 and TNF-α in the model group were significantly higher than those in the blank control group (P<0.05)， and the contents of IL-1β， TNF-α in the yiceng group were significantly lower than those in the model group (P<0.05). The contents of IL-4 in the model group were significantly higher than those in the blank control group (P<0.05)， and the contents of IL-10 and TGF-β in the model group were significantly lower than those in the blank control group (P<0.05)， The contents of IL-10 in the yiceng group were significantly higher than those in the model group (P<0.05).the content of HMGB1，α-SMA，TIMP1，Collagen Ⅰ and Collagen Ⅲ protein and genelevel expressed in the model group were significantly higher than the blank group （P<0.05）; The content of HMGB1、α-SMA、TIMP1、Collagen Ⅰ and Collagen Ⅲ protein and gene level expression in the yiceng group were significantly lower than the model group（P<0.05）. CONCLUSION Yiceng can inhibit synovial fibrosis may be related to the inhibition of HMGB1 and the balance of pro-inflammatory and anti-inflammatory factors.