This study aimed to determine the effects of dietary aged maize with supplementation of different levels of oxidized fish oil on growth performance, nutrient digestibility, serum antioxidant activity and gut health in piglets. Forty-two piglets were arranged in 2 × 3 factorial treatments in a complete randomized block design with seven replicates per treatment and one pig per replicate for 28 d. Diets included twp types of maize (normal maize or aged maize) and three levels of oxidized fish oil (OFO) (3% non-oxidized fish oil (0% OFO), 1.5% OFO and 1.5% non-oxidized fish oil (1.5% OFO), and 3% OFO (3% OFO). Results showed that dietary aged maize did not affect growth performance, diarrhea, and the apparent total tract digestibility (ATTD) of nutrients in piglets ( > 0.05). However, aged maize increased malonaldehyde (MDA) content and decreased total antioxidant capacity (T-AOC) in serum on both 14th and 28th days ( < 0.05) compared to the normal maize groups. Meanwhile, compared with normal maize, dietary aged maize showed a slight, but not significant ( > 0.10) decrease in total superoxide dismutase (T-SOD) activity and VE content in serum on the 14th day. In addition, aged maize significantly decreased mRNA expression ( < 0.05) and tended to increase ( < 0.10) and mRNA expression in jejunal mucosa. Compared with non-oxidized fish oil, oxidized fish oil resulted in the decrease of the 14-28 d and 0-28 d ADG, as well as the ATTD of dry matter (DM), ether extract (EE), organic matter (OM) ( < 0.05), whereas the increase in diarrhea index ( < 0.05) and F/G of the whole period ( < 0.05). Oxidized fish oil decreased serum T-AOC on both the 14th and the 28th days ( < 0.05), and decreased serum T-SOD activity and VE content on the 28th day ( < 0.05), whereas increased serum MDA content on the 28th day ( < 0.05) and 14th day ( < 0.10) compared with fresh fish oil. Meanwhile, ( < 0.05) and ( < 0.10) mRNA expression in jejunal mucosa were decreased compared with non-oxidized fish oil. In addition, dietary oxidized fish oil tended to decrease 14-28 d ADFI and the ATTD of CP ( < 0.10), and piglets fed oxidized fish oil significantly decreased 14-28 d ADFI, the ATTD of CP, and mRNA expressions in jejunal mucosa when piglet also fed with aged maize ( < 0.05). Collectively, these results indicated that dietary oxidized fish oil decreased growth performance and nutrients digestibility of piglets fed with aged maize. This nutrient interaction may be mediated by inhibiting intestinal nutrient transporter, inducing intestinal inflammation, and reducing antioxidant capacity.