Abstract: Objective To explore the occurrence of oxidative stress and antioxidases expression in diaphragm of severely burned rats, so that the mechanism of respiratory muscle atrophy and dysfunction post-burn injury will be further clarified. Methods Eighty male Wistar rats (aged 7 to 8 weeks) were divided into sham injury group and burn injury group according to the random number table, with 40 rats in each group. Rats in burn injury group were inflicted with 50% total body surface area full-thickness scald (hereinafter referred to as burn) on the back and abdomen by immersing into 80 ℃ water for 15 s and 8 s respectively. Immediately after injury, 40 mL/kg normal saline was injected through abdomen for resuscitation, and the wounds were treated with iodine. Except for immersing into 37 ℃ warm water and no resuscitation, the other treatments of rats in sham injury group were the same as those of burn injury group. Whole diaphragms of 8 rats per time point per group were collected after anesthesia at post injury hour (PIH) 2 and on post injury day (PID) 1, 3, 7, and 14, and muscle mass was determined. The protein carbonyl content was determined by microplate reader. The protein expressions of catalase, superoxide dismutase 2 (SOD2), and glutathione peroxidase 1 were determined by Western blotting. Data were processed with analysis of variance of factorial design, t test, and Bonferroni correction. Results (1) There were no statistically significant differences in the diaphragm mass of rats between the 2 groups at PIH 2 and on PID 1 (t=0.453, 0.755, P>0.05). The diaphragm mass of rats in burn injury group started to decrease from PID 3, which was significantly lower than that of sham injury group (t=3.321, P<0.01). The diaphragm mass of rats in burn injury group started to increase from PID 7 to PID 14, which was significantly lower than that of sham injury group (t=4.622, 4.380, P<0.01). (2) Protein carbonyl content in diaphragm of rats in burn injury group at PIH 2, and on PID 1, 3, 7, and 14 [(2.7±0.3), (2.5±0.5), (2.4±0.4), (2.5±0.4), (3.2±0.6) pg/mL] was significantly higher than that of sham injury group respectively [(1.2±0.4), (1.6±0.3), (1.5±0.7), (1.7±0.3), (1.8±0.4) pg/mL, t=5.994, 3.263, 3.666, 3.158, 5.763, P<0.05 or P<0.01]. (3) Protein expressions of catalase in diaphragm of rats in burn injury group on PID 1 and 3 were close to those of sham injury group (t=0.339, 0.324, P>0.05). There were no statistically significant differences in protein expressions of SOD2 in diaphragm of rats between the 2 groups at PIH 2 and on PID 1, 3, 7, and 14 (t=1.446, 1.385, 0.757, 1.561, 0.531, P>0.05). There were no statistically significant differences in protein expressions of glutathione peroxidase 1 in diaphragm of rats in the 2 groups at PIH 2 and on PID 1, 3, and 7 (t=0.200, 0.729, 0.385, 1.559, P>0.05). Conclusions Continuous oxidative stress and relatively insufficient expression of antioxidases in diaphragm induced by burn injury could be a contributor to diaphragm atrophy.