A novel sugar ester poacynose (1) was isolated from the flowers of Poacynum hendersonii together with 31 known compounds. The structure of 1 was established mainly on the basis of 1D and 2D NMR spectral data. Among the isolates, several constituents, such as kaempferol 3-O-sophoroside (5), picein (16), and 4-hydroxybenzoic acid 4-O-β-D-glucopyranoside (17) moderately promoted adipogenesis of 3T3-L1 cells. In addition, simultaneous quantitative analysis of eight flavonoid constituents from the flower and leaf parts of P. hendersonii was developed.