Phytochemical constituents have been participated with essential role in the discovery of several clinically effective anticancer agents. The goal of this study was to isolate phytoconstituents from Koelreuteria elegans twigs (Sapindacea family) and evaluate their anticancer activities against human lung, colon and breast carcinoma cell lines. The aqueous methanol extract of plant's twigs was fractionated with different solvents and the preliminary cytotoxicity of fractions was determined using brine shrimp lethality assay. Nine compounds from K. elegans twigs butanol fraction were isolated for the first time; gallic acid (1), methyl gallate (2), 6-O- [Galloyl 4- methyl ether]-(α/β)-D-glucopyranose (3), 3, 5-di-O-galloylquinic acid butyl ester (4), 3,4,5-tri-O-galloylquinic acid butyl ester (5), 1,3,4,5-tetra-O-galloylquinic acid butyl ester (6), two isomers of 3-O-galloyl quinic acid butyl ester and 4-O-galloyl quinic acid butyl ester (7), austrobailignan 1 (8) and β-sitosterol (9). The structures of compounds were elucidated using different spectroscopic techniques. Anticancer activities of butanol fraction, methyl gallate and austrobailignan 1were estimated in-vitro by cell viability assay. The results showed significant anticancer activity of both methyl gallate and austrobailignan 1 against breast carcinoma cell lines and less cytotoxicity against colon carcinoma cell lines while almost no activity against lung carcinoma cell lines.