From the ethanol extract of the whole plant of Ageratum conyzoides L. (Compositae), one new chromene, 2,2-dimethylchromene 7-methoxy-6-O-beta-D-glucopyranoside, was isolated, together with thirteen known compounds, seven of which were being reported for the first time. The compounds were all characterized by MS, IR, 1D- and 2D-NMR spectroscopy. 7,3',5'-Tri-O-methyltricetin (7), precocene II (9), 3,5,7,4'-tetrahydroxyflavone (13) and 5,6,7,3',4',5'-hexamethoxyflavone (14) exhibited inhibitory activity on the P-388 cancer cell line with IC50 values of 12.8, 24.8, 3.5 and 7.8 microM respectively, while compound 9 exhibited inhibitory activity on the HT-29 cancer cell line with an IC50 value of 61 microM; the others showed no significant cytotoxic activity on the cell lines tested.