Seven isoprenylated flavonoids were isolated from Artocarpus styracifolius, including one new triisoprenylated flavone, styracifolin D (1,) and six known ones, artocarpone B (2), kuwanon C (3), 6-C-prenyl luteolin (4), albanin A (5), 2,4,2',4'-tetrahydroxy-3'-(3-methyl-2-butenyl)-chalcone (6), and 3'-[γ-hydroxymethyl-(E)- γ-methylallyl]-2,4,2',4'-tetrahydroxychalcone 11'-0-coumarate (7). The structures of these compounds were determined by analysis of their spectroscopic and mass spectrometric data. Of them, 3 and 5 exhibited inhibitory effects on cathepsin K with IC(50) values of 114.6 and 7.4 μM, respectively.