Objective:To explore the effect of low intensity pulsed ultrasound(LIPUS)on inhibiting the abnormal cell phenotype of fibroblast-like synoviocytes in rheumatoid arthritis(RA-FLS)and possible mechanism. Method:Synoviocytes were isolated by using enzyme digestion,and the morphology of cells was observed un-der microscope.At the same time,the expression of Vimentin protein was detected by immunofluorescence method to identify RA-FLS.Cells cultured in vitro were divided into four groups:control group,LIPUS group,tumor necrosis factor(TNF-α)group and TNF-α+LIPUS group or three groups:control group,interleu-kin-6(IL-6)group and IL-6+LIPUS group.The effects of LIPUS on RA-FLS cell viability and proliferation were detected by CCK8 and EDU assay respectively,and the effects of LIPUS on RA-FLS migration were ob-served by scratch test and Transwell migration assay.RT-qPCR was used to detect the gene expression of im-portant cytokines,chemokines and matrix metalloproteinases(MMPs)in RA-FLS.ELISA was used to further detect the effect of LIPUS on the expression of IL-6,a key effector of RA-FLS,and the effects of LIPUS on mitogen-activated protein kinase(MAPK)signaling pathway in RA-FLS were detected by Western Blot. Result:Purified RA-FLS were obtained.Firstly,LIPUS could suppress the cell activity(P＜0.00l)and prolifer-ation(P=0.007)induced by TNF-α in RA-FLS cultured in vitro.However,the migration and the transcription levels of MMPs related to migration(MMP2 and MMP9)were not significantly different between groups(P＞0.05).LIPUS could inhibit the high expression of IL-6 and interleukin-8(IL-8)at the mRNA level in the in-flammatory environment induced by TNF-α(P＜0.001),but there was no significant difference in the suppres-sion of interleukin-1β(IL-1β),MMP1 and MMP13(P＞0.05).In addition,compared with untreated group,LI-PUS could inhibit the secretion of IL-6 in RA-FLS induced by TNF-α(P＜0.001),and also inhibited the pro-liferation of RA-FLS induced by IL-6(P-0.003).Finally,LIPUS could inhibit the phosphorylation of p38 MAPK and c-Jun N-terminal kinase(JNK)in MAPK signaling pathway(P=0.033),but the effect on the phosphorylation of extracellular signal-regulated kinas 1/2(ERK1/2)was not significantly(P＞0.05). Conclusion:LIPUS could reduce the abnormal proliferation of RA-FLS in inflammatory state without affecting its migration,which might be related to the inhibition of p38/JNK-IL-6 signaling pathway.