Abnormal activation of histone deacetylases (HDACs) is associated with tumorigenesis and/or tissue dysplasia.Some HDAC inhibitors have been developed and used in clinical practice.In this study,eleven compounds from the 70% ethanol extract of Epimedium sagittatum,a Chinese herbal medicine with bone strengthening effect,were obtained under the guidance of bioassays using the HDAC inhibitor screening kits.Based on the analyses of NMR and MS data,chemical structures of these compounds were identified as quercetin (1),vitexin (2),kaempferol-3-O-α-L-arabinopyranoside (3),kaempferol-3-O-β-D-xylopyranoside (4),kaempferol-3-O-β-D-glucopyranoside (5),kaempferol-3-O-(6″-O-acetyl)-β-D-glucopyranoside (6),kaempferol-3-O-(6″-O-(E)-p-coumaroyl)-β-D-glucopyranoside (7),kaempferol-3-O-(2″,4″-di-O-(E)-p-coumaroyl)-β-D-glucopyranoside (8),isorhamnetin-3-O-β-D-glucopyranoside (9),isorhamnetin-3-O-β-D-xylopyranoside (10),and schizandriside (11).Among them,2-11 were natural products identified from this plant for the first time;1-10 exhibited stronger than icariin the activities in inhibiting HDAC;and 3-5 exhibited stronger than kaempferol the activities in inhibiting HDAC.Effects of 3-5 on the expression of HDAC1-11 in HeLa cells were further investigated by Western blotting.It was found that,all of the three compounds strongly inhibited the expression of HDAC6,and 4 also inhibited the expression of HDAC4/7.HDAC4,6 and 7 are repressers of osteoblast differentiation and bone formation.In summary,our data revealed for the first time the components from Epimedium sagittatum that have HDAC inhibitory activities:isopentene-free flavonoids,especially kaempferol-3-O-monoglycosides (3-5).The results that compounds 3-5 inhibited the expression of HDAC6 and/or HDAC4/7 provided preliminary experimental evidences to identify those compounds a structurally characteristic of kaempferol-3-O-monoglycoside as potential anti-osteoporotic constituents in Herba Epimedii.