Chemical investigation of Cassia grandis leaves resulted in the isolation of the new 2-methoxy 6,7,2',6'-tetrahydroxy flavanone 6-O-β-glucoside together with the known flavonol glycosides, kaempferol-3-O-α-rhamnoside, and quercetin 3-O-α-rhamnoside. The structure assign ments were based on conventional analytical methods and confirmed by HRFTESIMS, 1H and 13C NMR, COSY, HSQC and HMBC data. The total phenolic content of the extract was estimated by Folin-Ciocalteu's method. The antioxidant capacity was investigated using DPPH radical scavenging assay. The ethyl acetate and the n-butanol fractions showed poor cytotoxic activity only at high concentrations against the three different cancer cell lines, hepatocellular (HepG-2), breast (MCF-7), and prostate (PC3) by the neutral red uptake assay.