To investigate the effects of miR-31 on TLR4/NF-κB signaling pathway and apoptosis-related proteins in dextran sulfate sodium (DSS) induced mouse colon colitis. Methods: ① Mouse model of colon colitis: 1% DSS was used to induce mouse ulcerative colitis (UC). Fourteen FVB non-transgenic mice were randomly divided into control group (n= 6), DSS group (n= 8), and 16 FVB miR-31 transgenic mice were randomly divided into miR-31 overexpression group (n= 8), miR-31 overexpression +DSS group (n= 8). DSS was dissolved in water and administered to mice by drinking water. The DSS group and miR-31+DSS group drank 1% DSS water in the first week, normal sterilized water in the second week, and 1% DSS water in the third week, after 5 weeks, the modeling was completed, then the colon tissues of the mice were collected. Western blot and IHC were used to detect the expressions of NF-κB p65, TLR4, Bax and Bcl-2 proteins in mouse colon tissue, TUNEL was used to detect apoptosis of mouse colon tissues. ② Cell culture experiments: Transfection of miR-31mimic and inhibitor by lipofectamine resulted in overexpression or knockdown of miR-31 in human colon epithelial cell line HCT 116 cells, each group was repeated three times and cells were collected 48 h later, Western blot was used to detect the expressions of NF-κB p65 and TLR4 protein. ① In animal experiments, compared with the control group, the expression levels of NF-κB p65, TLR4 protein and apoptotic cell index in the DSS group and miR-31 overexpression group in mouse colon tissue were significantly increased (P＜0.05 or P＜0.01), and the Bcl-2 / Bax ratio was significantly reduced (P＜0.05 or P＜0.01); and compared with the DSS group, the expression levels of NF-κB p65, TLR4 protein and apoptotic cell index in the miR-31+DSS group were significantly increased (P＜0.01), while the Bcl-2/Bax ratio was significantly decreased (P＜0.01). ② In cell experiments, compared with the control group, the expression levels of NF-κB p65 and TLR4 protein in the over-expressed miR-31 group of HCT 116 cells were significantly increased (P＜0.05 or P＜0.01), the expressions of NF-κB p65 and TLR4 protein in miR-31 knockdown group were decreased (P＜0.05). miR-31 promotes the development of colitis by promoting TLR4/NF-κB signaling pathway and mediating apoptosis of intestinal epithelial cells.