Background:Oxidative stress is a main cause of piglet gut damage and diarrhea. Pyrroloquinoline quinone (PQQ), is a novel redox cofactor with antioxidant properties. However, the effect and mechanism that PQQ supplementation decreases oxidative injury in weaned pigs is not understood. Therefore, the aim of this study is to confirm the effect of PQQ on regulating redox status in weaned pigs and the mechanism for antioxidant function by porcine intestinal epithelial cell line (IPEC-J2) challenged with H2O2. Results:Experiment 1, 144 Duroc × Landrace × Yorkshire pigs (weaned at 28 d) were allocated to four groups:received a basal diet (control) and diets supplemented with 0.15％, 0.30％and 0.45％PQQ, respectively. On d 28, growth performance, diarrhea incidence and redox factors were measured. Experiment 2, IPEC-J2 were treated with or without PQQ in the presence or absence of H2O2 for indicated time points. Experiment 3, IPEC-J2 were transfected with or without Nrf2 siRNA, then treated according to Experiment 2. The cell viability, redox factors, protein of tight junctions and Nrf2 pathway were determined. In vivo, PQQ supplementation demonstrated dose-related improvements in average daily gain, and gain to feed ratio (Linear P<0.05). During d 0–28, compared to controls, 0.45％PQQ supplementation for pigs decreased diarrhea incidence and MDA content in liver and jejunum, and increased concentration of SOD in liver;0.3％PQQ supplementation decreased ileal and liver MDA concentration;and 0.15％PQQ supplementation decreased ileal MDA concentration (P<0.05). In vitro, compared to cells cultured with H2O2, pre-treatment with PQQ increased cell viability, tight junction proteins expression including ZO-1, ZO-2, Occludin and Claudin-1;and decreased ROS concentration and level of Caspase-3 (P<0.05);as well as upregulated the ratio of Bcl-2 to Bax and protein expression of nuclear Nrf2, HO-1. Notably, Nrf2 knockdown by transfection with Nrf2 siRNA largely abrogated the positive effects of PQQ pretreatment on H2O2-induced intracellular changes. Conclusions:PQQ administration attenuated oxidative stress in weaned pigs which is associated with activation of Nrf2/HO-1 pathway.