The anti-cancer activity of garlic mainly arises due to the presence of various organosulfur compounds including diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS). Herewith, we report a number of 4-substituted benzyl analogs of DADS and their selenium counterparts for a detailed structure-activity relationship towards their anti-proliferative activities in human breast cancer cell lines. Disulfide having 4-cyano group exhibited highest activity among all disulfides. In contrast, all diselenides exhibited very good anti-proliferative activities than DADS. Furthermore, unlike disulfides, diselenides were more selective towards cancer cells over normal cells. Some active compounds were further tested for their activities in some organ specific cell lines such as HepG2, PC-3 and HCT-116 to understand their efficacy. Elevated level of intracellular reactive oxygen species (ROS) by most of the benzyl diselenides reveals a possible mode of their action. Therefore, this study indicates that the anti-proliferative activity of DADS can be significantly enhanced upon suitable structural modifications. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim