Recent analysis of air samples from Chicago and Lake Michigan areas observed a ubiquitous airborne polychlorinated biphenyl (PCB) congener, 3,3′-dichlorobiphenyl (PCB11). Our analysis of serum samples also revealed the existence of hydroxylated metabolites of PCB11 in human blood. Because PCBs and PCB metabolites have been suggested to induce oxidative stress, this study sought to determine whether environmental exposure to PCB11 and its 4-hydroxyl metabolite could induce alterations in steady-state levels of reactive oxygen species (ROS) and cytotoxicity in immortalized human prostate epithelial cells (RWPE-1). This study also examines if antioxidants could protect the cells from PCB11-induced cytotoxicity. Exponentially growing RWPE-1 cells were exposed to PCB11 and its metabolite, 3,3′-dichlorobiphenyl-4-ol (4-OH-PCB11), as well as an airborne PCB mixture resembling the Chicago ambient air congener profile, every day for 5 days. Results showed that 4-OH-PCB11 could significantly induce cell growth suppression and decrease the viability and plating efficiency of RWPE-1 cells. 4-OH-PCB11 also significantly increased steady-state levels of intracellular superoxide, O2 •−, as well as hydroperoxides. Finally, treatment with the combination of polyethylene glycol–conjugated CuZn superoxide dismutase and catalase added 1h after 4-OH-PCB11 exposures, significantly protected RWPE-1 cells from PCB toxicity. The results strongly support the hypothesis that exposure to a hydroxylated metabolite of PCB11 can inhibit cell proliferation and cause cytotoxicity by increasing steady-state levels of ROS. Furthermore, antioxidant treatments following PCBs exposure could significantly mitigate the PCB-induced cytotoxicity in exponentially growing human prostate epithelial cells.