OBJECTIVE It is demonstrated that excessive activation of NF-κB is central to the pathogenesis of inflammatory bowel disease (IBD). Zinc finger protein A20 (A20) is a key player in the negative feedback regulation of NF-κB signaling in response to multiple stimuli and has been described as central gatekeeper in inflammation and immunity. Mice genetically deficient in A20 develop severe intestinal inflammation and have increased susceptibility to dextran sodium sulfate (DSS)-induced colitis. Few studies have been done to explore the role of A20 in the pathogenesis of IBD. To clarify the relationship between intestinal inflammation and the expression level of A20 in IBD patients, the expression level of A20 and a series of inflammatory cytokines, such as NF-κB, IL-6, and IL-8, in children with IBD and controls were examined. METHODS Terminal ileal mucosal samples were obtained via endoscopy. Fifty-seven mucosal samples were divided into 4 groups: normal control group (n = 16), IBD remission group (n = 12), IBD active group (n = 13) and non-IBD enteritis group (n = 16). According to disease activity index scores, the IBD patients were divided into IBD remission group and IBD active group. Normal control group was consisted of patients with functional bowel disorders or intestinal polyps. Non-IBD enteritis was defined as changes in which endoscopy and histological examination showed inflammatory changes but could not be diagnosed as IBD. Real-time PCR was adopted for detecting the mRNA levels of A20, IL-6 and IL-8. Meanwhile immunohistochemistry was performed to measure the expression of A20 and NF-κB. RESULTS (1) The expression of A20 and NF-κB were very low in normal control group, but significantly up-regulated in IBD active group and non-IBD enteritis group (P < 0.01 for both); (2) Compared with normal control group, expression of NF-κB [(9.35 ± 4.84)% vs. (0.57 ± 0.44)%, P < 0.01], IL-6 (t' = 1.34, P > 0.05), IL-8 (t = 1.38, P > 0.05) increased in IBD remission group, while the expression of A20 in both mRNA (t = 1.03, P > 0.05) and protein levels [(0.36 ± 0.18)% vs. (0.87 ± 0.29)%, P < 0.01] decreased; (3) Compared with non-IBD enteritis group, although the expression of NF-κB [(24.17 ± 11.27)% vs. (55.29 ± 21.84)%, P < 0.01], IL-6 (t = 2.22, P < 0.05), IL-8 (t = 2.97, P < 0.01) were highly increased in IBD active group, the expression of A20 in both mRNA(t = 2.26, P < 0.05) and protein levels [(29.23 ± 11.70)% vs. (16.81 ± 5.90)%, P < 0.01]significantly decreased; (4) The expression of IL-6, IL-8 were similar in IBD remission group and non-IBD enteritis group (both P > 0.05), but the expression of A20 was much lower in both mRNA (t = 4.42, P < 0.01) and protein levels [(29.23 ± 11.70)% vs. (0.47 ± 0.25)%, P < 0.01] in IBD remission group. CONCLUSIONS The results demonstrate that there is an excessive inflammatory response but insufficient up-regulation of A20 expression in IBD patients. Low levels expression of A20 may play an important role in the pathogenesis of IBD.