Lectins are proteins or glycoproteins able to recognize and bind to specific carbohydrates of cell surface. These lectins properties are responsible for triggering various biological effects, including the ability to kill malignant cell at relatively low concentrations.  In this study, CySeL₁, an isoform of Capparis yco seed lectin, induced apoptotic cell death in Walker 256 tumor cells in vitro. The percentage of apoptotic tumor cells measured by flow cytometry, using annexin V, was 30% after 4h of incubation with CySeL₁. Indeed, apoptotic cell death was mediated by caspase-3 activation. Levels of cytosolic free Ca⁺² concentrations ([Ca⁺²]_cytosol), measured by flow cytometry, using Fluo 3-AM, were higher in tumor cells treated with CySeL₁. Chelation of intracellular Ca⁺² with BAPTA partially protected W256 cells from CySeL₁-induced decrease in proliferation and viability. This indicates that high [Ca⁺²]_cytosol mediates cell death. FK506 and cyclosporin A also protected W256 cells against the apoptotic effects of CySeL₁. The protective effect of FK506 was higher than that caused by cyclosporin A. This indicates that a parallel rescue pathway via calcineurin, a phosphatase sensitive to cyclosporin A or FK506, mediated cell death caused by CySeL₁. In addition, CySeL₁ induced an increase of reactive oxygen species (ROS) generation and disruption of the mitochondrial membrane potential (Δψ_m). ROS generation by W256 tumor cells measured with dichlorodihydrofluorescein diacetate (H₂DCF-DA) was 3-fold higher in CySeL₁ treated cells. Mitochondrial membrane potential (Δψ_m) estimated as normalized fluorescence (F/F_CCCP) of DioC₆(3) was lower in CySeL₁ treated cells (F/F_CCCP = 3) as compared to control (F/F_CCCP = 7). These data adds to the understanding on the apoptotic pathway activated by lectins.