Abstract: The chemical constituents of Cydonia oblonga (Quince) seeds were investigated using chromatographic methods, including silica gel, Sephadex LH-20 and semi-preparative-HPLC. Eleven compounds were isolated and their structures were elucidated on 1D or 2D NMR, and HR-ESI-MS. These analyses have lead to identification of 5,7-dihydroxy-2-n-pentacosanyl chromen-4-one (1), ursolic acid (2), tormentic acid (3), oleanolic acid (4), β-daucosterol (5), β-sitosterol (6), amygdalin (7), rutin (8), kaempferol (9), quercetin (10) and isoquercitrin (11). Among these, compound 1 is a new compound, and compounds 3, 5 were isolated from this plant for the first time. Compounds 1-4 and 8 showed significant PTP1B inhibitory activities with IC₅₀ value of 0.465, 16.14, 28.96, 23.78 and 11.70 μmol·L^-1, respectively.