Abstract: This study was designed to evaluate the effects of Diquat-induced oxidative stress on tryptophan catabolism in weaned pigs. According to a single factorial arrangement, a total of 24, Landrance ×Yorkshire weaned piglets were assigned into three treatments of 8 animals each, consisting of pigs given ad libitum access to feed (control), challenged with diquat (10 mg·kg^-1 BW) and given ad libitum access to feed (oxidative stress), or pair-fed to receive the same amount of feed as the Diquat-challenged pigs (pair-fed). The trial lasted for 7 days. The results showed that: ⑴ The growth performance and activities of SOD (superoxide dismutase) (P<0.01) and GPx (glutathione peroxide dismutase) (P<0.01)significantly declined in Diquatchallenged pigs, which followed by increased serum malondialdehyde (MDA) (P<0.01); ⑵ Diquat-induced oxidative stress decreased serum free Trp (tryptophan), augmented serum Kyn (kynurenine) (P<0.05 or P<0.01), Kyn/Trp (P<0.01) and 5-HT (5-hydroxytryptamine) (P<0.05); ⑶ After Diquat injection, the liver TDO (tryptophan 2,3-dioxygenase) activities including total activity(P<0.05),holoenzyme(P<0.05) and apoenzyme activity(P<0.05) were enhanced, the effect of oxidative stress on IDO (indolamine 2,3dioxygenase) was no significant difference. These results suggested that Diquat-induced oxidative stress increased catabolism of tryptophan by augmenting TDO activity in weaned pigs.