2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) are persistent organic pollutants which coexist in environment, and human are co-exposed to these chemicals. Our present study was aimed to investigate the possible enhanced nonalcoholic fatty liver disease (NAFLD) in ApoE−/− mice co-exposed to TCDD and PCBs and to reveal the potential mechanisms involved in. Male ApoE−/− mice were exposed to TCDD (15 μg/kg) and Aroclor1254 (55 mg/kg, a representative mixture of PCBs) alone or in combination by intraperitoneal injection four times over a 6-week period. Those mice co-exposed to PCBs and TCDD developed serious liver steatosis, necrosis, and inflammatory stimuli. Interestingly, all treatment induced hepatic cytochrome P450 1A1 (CYP1A1) expression, but the maximal level of CYP1A1 was not observed in the co-exposure group. Furthermore, microarray analysis by ingenuity pathway analysis software showed that the nuclear factor-erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress response pathway was significantly activated following co-exposure to TCDD and PCBs. Our data demonstrated that co-exposure to TCDD and PCBs markedly worsen NAFLD in ApoE−/− mice. © 2014 Wiley Periodicals, Inc. Environ Toxicol 30: 1364–1374, 2015.