This experiment was conducted to investigate the effects tea tree oil (TTO) on antioxidant indices in serum, liver and intestinal mucosa of weaned piglets. One hundred and twenty 21-day-old "Duroc×Landrace×Yorkshire" hybrid weaned piglets with similar body weight of[(6.73±0.12) kg] were selected and randomly assigned to 5 groups with 6 replicates per group and 4 piglets per replicate. The five groups were as follows:control group (CON group, fed a basal diet), antibiotic group[ANT group, fed the basal diet+200 mg/kg colistin (10%)+75 mg/kg chlortetracycline (15%)], low tea tree oil group (LTO group, fed the basal diet+50 mg/kg tea tree oil), middle tea tree oil group (MTO group, fed the basal diet+100 mg/kg tea tree oil) and high tea tree oil group (HTO group, fed the basal diet+150 mg/kg tea tree oil). The experiment lasted for 21 days. The results showed as follows:1) the serum total-antioxidant capacities(T-AOC) of piglets of HTO group was significantly higher than that of LTO and MTO groups (P<0.05), the serum superoxide dismutase (SOD) activity of piglets of MTO group was significantly higher than that of HTO, CON and ANT groups (P<0.05), the serum hydrogen peroxide (H₂O₂) content of piglets of LTO group was significantly lower than that of MTO, HTO and CON groups (P<0.05). 2) Compared with the CON and ANT groups, the liver T-AOC of piglets of LTO, MTO and HTO groups was significant increased (P<0.05), the glutathione peroxidases (GSH-Px) activity and H₂O₂ content in liver of piglets of LTO and MTO groups were significant increased (P<0.05), the liver glutathione (GSH) content of piglets of HTO group was significant increased (P<0.05). Compared with the CON group, the liver SOD activity of piglets of LTO and MTO groups were significant increased (P<0.05). 3) The activities of GSH-Px and SOD in jejunum mucosa of piglets were significantly higher than those of ANT group (P<0.05), the jejunum mucosa H₂O₂ content of piglets of LTO, MTO and HTO and ANT groups was significantly lower than that of CON group (P<0.05). 4) The SOD activity and GSH content in ileum mucosa of piglets of HTO group were significantly higher than those of CON group (P<0.05), the ileum mucosa MDA content of piglets of LTO, MTO and HTO and ANT groups was significantly lower than that of CON group (P<0.05). It is concluded that tea tree oil can improve the activities of antioxidant enzyme in serum, liver and intestinal mucosa, and decrease the content of H₂O₂ in serum and jejunum mucosa of weaned piglets, thus improve the antioxidant ability of weaned piglets, and the general effect was better than antibiotics, the recommend additive amount of tea tree oil is 100 mg/kg.