To study the effect of jejunal immune related indexes and villus structure changes in flufenicol-induced diarrhea in broilers.After 7 days of adaptive feeding, a total of 40 1-day-old broilers were randomly divided into control group, flunfenicol group (drinking water supplemented with 100 mg·(kg?d)^-1 flunfenicol to 35 days of age). At 35 days of age,the weight,spleen and thymus index were detected,jejunal tissue was stained with HE and then were observed,the length of villus and the depth of crypt were measured and the ratio of villus to crypt was calculated.The relative expression of TLR4,MyD88,NF-κB and TNF-α in the jejunum were detected by real-time PCR.The results showed that compared with the control group,the flufenicol group's villus length and crypt ratio of jejunum extremely significant decreased(P<0.01),the crypt depth of jejunum extremely significant increased (P<0.01);the weight,spleen index and thymus index extremely significant decreased (P<0.01);the relative expression of TLR4,MyD88,NF-κB and TNF-α mRNA were extremely significant increased (P<0.01).The structural and functional changes of jejunal villi and the abnormal expression of immune-related indexes were involved in the occurrence and development of flufenicol-induced diarrhea in broilers.