AIM　The purpose is to investigate the Anti-inflammatory mechanism of Biota orientalis. METHODS　Using rat leukocytes and rabbit platelets as experimental material the biosynthesis of leukotriene, 12-hydroxyheptadecatrienoic acid(12-HHT) and 12-hydroxyeicosatetraenoic acid(12-HETE) in the cells was determined with HPLC. RESULTS　Biota orientalis was shown to inhibit the biosynthesis of leukotriene B4(LTB4) and 5-hydroxyeicosatetraenoic acid(5-HETE) with IC50 of 0.40 and 0.41　mg/ml crude herb, respectively. It was also displayed to inhibit biosynthesis of 12-HHT in the platelets. CONCLUSION　Biota orientalis leaves contain anti-inflammatory components and the anti-inflammatory mechanism was related with inhibiting metabolism of arachidonic acid.