OBJECTIVE： To investigate the improvement effect and mechanism of ethanol extract of Arenga pinnata on acute peritonitis model mice. METHODS： The mice were randomly divided into blank control group （distilled water）， model control group （distilled water）， positive control group （Loxoprofen sodium tablets 0.023 g/kg） and ethanol extract of A. pinnata high- dose， medium-dose and low-dose groups （6.5， 3.25， 1.625 g/kg， by the amount of extract） according to body weight， with 24 mice in each group. They were given relevant medicine intragastrically for consecutive 3 d. 30 min after last administration， except for blank control group， other groups were given zymosan solution intraperitoneally to induce acute peritonitis model. The activity， response and excretion of mice were observed within 4 h after intraperitoneal injection of zymosan solution. 12 mice of each group were given Evans blue staining solution immediately after modeling. Peritoneal fluid was collected to observe the permeability of abdominal capillary in mice. Within 4 h after intraperitoneal injection of zymosan solution， total number of white blood cells in residual mice was counted in each group. ELISA assay was adopted to determine the contents of inflammatory factors （IL-1β， IL-6， IL-10， TNF-α， MPO）. RESULTS： Compared with blank control group， model control group suffered from significant writhing， abdominal retraction， crouch and diarrhea； peritoneal capillary permeability increased significantly （P＜0.01）. The total number of leukocyte and the contents of IL-1β， IL-6， IL-10， TNF-α and MPO in peritoneal fluid were increased significantly （P＜0.01）. Compared with model control group， above phenomena of mice occurred occasionally in positive control group， ethanol extract of A. pinnata high-dose， medium-dose and low-dose groups， and peritoneal capillary permeability decreased significantly （P＜0.01）. Total number of leukocyte and the contents of IL-1β and TNF-α in peritoneal fluid were decreased significantly （P＜0.05 or P＜0.01）， while IL-10 content was increased significantly （P＜0.05 or P＜0.01）. The contents of IL-6 and MPO in peritoneal fluid were decreased significantly in ethanol extract of A. pinnata high-dose and medium-dose groups （P＜0.05 or P＜0.01）， in dose-dependent manner. CONCLUSIONS： Ethanol extract of A. pinnata has improvement effect on acute peritonitis mice， the mechanism of which may be associated with reducing the permeability of abdominal capillaries， inhibiting inflammatory cell infiltration and regulating the secretion of inflammatory factors in abdominal cavity.