Abstract The present study was undertaken to determine whether sulforaphane-derived reactive oxygen species (ROS) might cause growth arrest and apoptosis in human bladder cancer 5637 cells. Our results show that the reduced viability of 5637 cells by sulforaphane is due to mitotic arrest, but not the G2 phase. The sulforaphane-induced mitotic arrest correlated with an induction of cyclin B1 and phosphorylation of Cdk1, as well as a concomitant increased complex between cyclin B1 and Cdk1. Sulforaphane-induced apoptosis was associated with the activation of caspase-8 and -9, the initiators caspases of the extrinsic and intrinsic apoptotic pathways, respectively, and activation of effector caspase-3 and cleavage of poly (ADP-ribose) polymerase. However, blockage of caspase activation inhibited apoptosis and abrogated growth inhibition in sulforaphane-treated 5637 cells. This study further investigated the roles of ROS with respect to mitotic arrest and the apoptotic effect of sulforaphane, and the maximum level of ROS accumulation was observed 3h after sulforaphane treatment. However, a ROS scavenger, N-acetyl-L-cysteine, notably attenuated sulforaphane-mediated apoptosis as well as mitotic arrest. Overall, these results suggest that sulforaphane induces mitotic arrest and apoptosis of 5637 cells via a ROS-dependent pathway.