ABSTRACT OBJECTIVE：To study the improvement effect of Periplaneta americana extract Ento-A on damp-heat ulcerative colitis（UC）model rats. METHODS：Totally 70 rats were randomly divided into normal control group（n＝8）and modeling group （n＝62）. The damp-heat UC model was induced in modeling group by high sugar，high fat，spicy diet combined with 2，4， 6-trinitrobenzene sulfonic acid enema. 48 modelrats were randomly divided into model control group，mesalazine group （300 mg/kg），Changyanning group（300 mg/kg）and Ento-A low-dose，medium-dose and high-dose（50，100，200 mg/kg，calculated by the extract），with 8 rats in each group. Normal control group and model control group were given normal saline intrsgastrically，and other groups were given relevant medicine intragastrically，once a day，for consecutive 14 days. After last administration， disease activity index （DAI）， colonic mucosal injury index （CMDI） and histopathological score （HS）of rats were determined. The spleen index，liver index and colon index in rats were determined. The serum levels of IL-8，IL-17，SOD and MDA，colonic levels of IL-2，PGE2 and MPO were detected by ELISA. RESULTS：Compared with normal control group，the DAI score，CMDI score，HS score，colonic index，the serum levels of IL-8，IL-17 and MDA， colonic levels of MPO and PGE2 were increased significantly（P＜0.01）；serum level of SOD and colonic level of IL-2 were decreased significantly （P＜0.01）. Compared with model control group，DAI score，CMDI score，serum levels of IL-17 and MDA，colonic levels of PGE2 were decreased significantly in Ento-A high-dose groups（P＜0.05 or P＜0.01），while serum level of SOD and colonic level of IL-2 were increased significantly（P＜0.01）. CMDI score and HS score，serum levels of IL-8，IL-17 and MDA，colonic levels of PGE2 and MPO were decreased significantly in Ento-A medium-dose group（P＜0.05 or P＜0.01）， while colonic level of IL-2 was increased significantly（P＜0.01）. HS score，serum levels of IL-17 and MDA，colonic levels of MPO and PGE2 were decreased significantly in Ento-A low-dose group（P＜0.05 or P＜0.01），while serum level of IL-2 was increased significantly（P＜0.01）. CONCLUSIONS：P. americana extract Ento-A may play improvement effect on damp-heat UC rats by regulating immune system balance and reducing inflammatory damage.