Although grape seed extract (GSE) has proven to be effective against various cancers, few studies have investigated the effects of GSE on human leukemia. In this study, we analysed the mechanisms involved in the apoptotic effects induced by GSE on human promyelocytic leukemia HL-60 cells. Thus, GSE treatment succeeded in activating caspase-3 (P < 0.05), the activation being dose-dependent and time-dependent. Activation of caspase-3 induced by GSE was accompanied by mitochondrial membrane depolarization (P < 0.05). Moreover, disruption of mitochondrial integrity caused by GSE treatment subsequently led to activation of caspase-9 (P < 0.05), and also produced a slight increase in ROS levels (P < 0.05). Cytotoxic effects elicited by GSE treatment ultimately resulted in extensive S-phase arrest (P < 0.05) and a substantial increase in the intrinsic rate of apoptosis (P < 0.05). Our findings suggest that the GSE induces apoptotic cell death and cell growth inhibition in human leukemic HL-60 cells, which seems to be dependent on mitochondrial damage. Therefore, the GSE obtained from Tempranillo cultivars could be an effective approach to restrain uncontrolled cell proliferation and survival in leukemia cells.