| [目的]This study investigated the protective effect of myo-inositol on oxidative damage of head kidney and spleen in young grass carp (Ctenopharyngodon idella) induced by Aeromonas hydrophila (A. hydrophila). [方法]A total of 540 grass carp (221.83±0.84g) were fed six diets with graded levels of myo-inositol [27.0(未添加),137.9,286.8,438.6,587.7和737.3 mg/kg] for 10 weeks. Subsequently, a challenge test was conducted by injection of A. hydrophila and the survival rated recorded for 14 days. [结果]The results indicated that compared with myo-inositol deficiency (basal diet, unsupplementation), optimal myo-inositol supplementation decreased Reactive oxygen species (ROS), malondialdehyde (MDA),and protein carbonyl contents (P < 0.05), and increased the activities and mRNA levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferased and glutathione reductase, and contents of glutathione (P < 0.05) in the head kidney and spleen under injection fish of A. hydrophila. Meanwhile, compared with myo-inositol deficiency (basal diet, unsupplementation), optimal myo-inositol supplementation up-regulated NF-E2-related factor 2 (Nrf2) mRNA and protein levels, and down-regulated Kelch-like ECH-associated protein-1 (Keap1) a and b mRNA levels in the head kidney and spleen under injection fish of A. hydrophila (P < 0.05). [结论]These results suggesting that optimal myo-inositol supplementation could protective fish head kidney and spleen structural integrity through increased antioxidative ability under injection fish of A. hydrophila. Finally, based on the antioxidant indices ROS content in the head kidney and spleen under injection fish of A. hydrophila, the myo-inositol requirement for young grass carp were estimated to be 452.1 and 449.0 mg/kg diet, respectively.