A series of 30 novel , disubstituted selenoureas were synthesized, characterized, and their antioxidant ability was tested using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid (ABTS) assays. Additionally, their cytotoxic activity was tested in vitro in a panel of three different cancer (breast, lung and colon) and two normal cell lines. Each selenourea entity contains a para-substituted phenyl ring with different electron-withdrawing and electron-donating groups, and different aliphatic and aromatic nuclei. All of the synthesized selenoureas present antioxidant capacity at high concentrations in the DPPH assay, and three of them (, and ) showed greater radical scavenging capacity than ascorbic acid at lower concentrations. These results were confirmed by the ABTS assay, where these novel selenoureas present even higher antioxidant capacity than the reference compound Trolox. On the other hand, 10 selenoureas present IC values below 10 µM in at least one cancer cell line, resulting in the adamantyl nucleus (-), the most interesting in terms of activity and selectivity. Outstanding results were found for selenourea , tested in the NCI60 cell line panel and showing an average GI of 1.49 µM for the 60 cell lines, and LC values ranging from 9.33 µM to 4.27 µM against 10 of these cancer cell lines. To gain insight into its anticancer activity mechanism, we investigated the cell cycle progression of the promising compound , as well as the type of programmed-cell death in a colon cancer cell line it provokes (HT-29). Compound provoked S phase cell cycle arrest and the induction of cell death was independent of caspase activation, suggesting autophagy, though this assertion requires additional studies. Overall, we envision that this compound can be further developed for the potential treatment of colon cancer.