The whole herb of Selaginella labordei Hieron.Ex Christ, a medicinal plant, is used in treatment of hepatitis, tumor and so on as traditional folk medicine in China.Lipoxygenase (LOX) exists in high expression in cancer tissue, and is involved in the pathologic process of inflammation, cancer and aging.Therefore, researching LOX inhibitor has latent important meaning for preventing and controling the development of inflammation and cancer.And we previously reported that the main activity fraction inhibiting LOX was the ethyl acetate extract of S.labordei.In this assay, we have further studied the lipoxygenase inhibition of the flavonoids isolated from the active fraction.Aim of study: LOX inhibitory activities of six flavonoid compounds from medicinal plants ofS.labordei are investigated.Materials and methods: six flavonoids have been isolated from the active fraction, and the 50% inhibitory concentration (IC50) of the each sample against LOX in vitro was determined, using a ultraviolet spectrophotometer with kinetics analysis software.Results: The six flavonoids all have obvious inhibitory action on lipoxygenase.Among them, two kinds of flavonoids were more active in inhibiting lipoxygenase than others, the IC50 ofamentoflavone was 7.03 μM and robustaflavone was 8.05 μM.Conclusions: Six flavonoids are active compounds in inhibiting lipoxygenase from S.labordei.