Oxidative stress has emerged as an important pathogenic factor in the development of breast cancer. Cholesterol-rich membrane rafts or lipid rafts (LRs) are reported to play an important role in oxidative stress-induced signal transduction. NADPH oxidase-dependent reactive oxygen species (ROS) production is implicated in oxidative stress in human mammary epithelial cells. In the present study, we determined the expression and regulation of membrane-bound subunits by LRs in human breast cancer cells. We report that basal levels of gp91phox and p22phox are expressed in breast cancer cells. We demonstrate for the first time that disruption of LRs resulted in the downregulation of NADPH oxidase subunits in breast cancer cells. Cholesterol depletion by 10 mM methyl-β-cyclodextrin (MβCD) translocated both gp91phox and p22phox out of LRs. Moreover, lipid raft disruption decreased NADPH oxidase activity (21.1 ± 0.5% in MCF-7 and 28.9 ± 1.0 in BT-549 cells), which was reversed by cholesterol repletion (95%). Therefore, the results suggest that the integrity of LRs plays an important role in the regulation of NADPH oxidase activity in breast cancer cells.