Five active compounds that inhibit cancer cells were isolated from adlay bran (Coix lachryma-jobi L. var. ma-yuen Stapf), and their structures and activities in vitro were characterized. The ethyl acetate-soluble fraction of methanol extracts of adlay bran (ABM-EtOAc) exhibited a stronger anti-proliferative effect on human lung cancer cell A549, human colorectal carcinoma cell HT-29, and COLO 205 than other fractions by MTT (3-4,5-dimethylthiazol-2-yl-2,5-diphenyl-tetrazolium bromide) assay. Assay-guided isolation gave five lactams including three that were previously undocumented; coixspirolactam A (1), coixspirolactam B (2), and coixspirolactam C (3); one isolated from the natural plant for the first time, coixlactam (4); and one known compound, methyl dioxindole-3-acetate (5). Pure active compounds were identified by spectral analysis including IR, 1H and 13C NMR, UV-vis, MS and 2D NMR techniques. All the compounds were tested for their anti-proliferative effect on A549, HT-29 and COLO 205 cells. These compounds showed anti-cancer activities with IC50 values between 28.6 and 72.6microg/mL.