Six flavonoid glycosides were isolated from the n-butanol fraction of cowpea seeds (Vigna sinensis K.) through silica gel ($SiO_2$) and octadecyl silica gel (ODS) column chromatographies. Based on their chemical structures determined via interpretation of spectroscopic data including NMR, MS, and IR, the compounds were identified as kaempferol 3-O-${eta}$-D-sophoroside (1), quercetin 3-O-${eta}$-D-sophoroside (2), isoquercitrin (3), hyperin (4), catechin 7-O-${eta}$-D-glucopyranoside (5), and quercetin 3-O-${eta}$-D-glucopyranosyl($1{ ightarrow}6$)-O-${eta}$-D-galactopyranoside (6). This is the first report of the isolation of these flavonoids from this plant. Among these flavonoids, compound 2, 5, and 6 significantly inhibited LDL oxidation exhibiting $96.0{pm}0.1$ ($IC_{50}:;3.9{mu}M$), $96.8{pm}1.7$ ($IC_{50}:;2.9{mu}M$), and $97.4{pm}0.1%$ ($IC_{50}:;3.5{mu}M$) inhibition, respectively, at a concentration of $40{mu}M$.