Seven flavonoids were isolated from the whole plants and fruits of Cayratia japonica through the activity-guided isolation of a methanol extract using a monoamine oxidase (MAO) inhibition assay as a monitor. The chemical structures of the isolates were assigned as $apigenin-7-O-{eta}-D-glucuronopyranoside$ (1), apigenin (2), luteolin (3), $luteolin-7-O-{eta}-D-glucopyranoside$ (4), (+)-dihydroquercetin (taxifolin) (5), (+)-dihydrokaempferol (aromadendrin) (6) and quercetin (7). Among the isolated compounds, flavones such as apigenin (2) and luteolin (3), as well as the flavonol, quercetin (7) showed potent inhibitory effects against the MAO activity with $IC_{50}$ values of 6.5, 22.6, and $31.6{mu}M$, respectively. However, the flavone glycosides, $apigenin-7-O-{eta}-D-glucuronopyranoside$ (1) and $luteolin-7-O-{eta}-D-glucopyranoside$ (4), showed mild MAO inhibition ($IC_{50}$ values: 81.7 and $118.6{mu}M$, respectively). The flavanonol derivatives, taxifolin (5) and aromadendrin (6), also showed weak inhibition ($IC_{50}$ values: 154.7 and $153.1{mu}M$, respectively). Furthermore, quercetin (7) had a more potent inhibitory effect on MAO-A ($IC_{50}$ value: $2.8{mu}M$) than MAO-B ($IC_{50}$ value: $90.0{mu}M$). Apigenin (2) and luteolin (3) also preferentially inhibited MAO-A ($IC_{50}$ values: 1.7 and $4.9{mu}M$, respectively) compared with MAO-B ($IC_{50}$ values: 12.8 and $59.7{mu}M$, respectively).