A new naturally occurring flavonol diglycoside, tamarixetin 3-O-β-glucopyranoside -7-O-α-rhamnopyranoside, was isolated along with two known flavonol diglycosides from the aerial parts of Tephrosia purpurea (L.) Pers. (Fabaceae). Bioassay guided fractionation of the light petroleum extract afforded two bioactive 5-deoxyflavones, pseudosemiglabrin and glabratephrin. Both showed cytotoxicity to the Hepg2 hepatic human cell line with IC50 values of 0.87 and 4.03 μg/mL, respectively. The isolated compounds were characterized by spectroscopic (UV, 1H, 13C, HMQC and HMBC NMR) and spectrometric (EI-MS, ESI-MS) analyses.