Abstract Objectives Determine xanthine oxidase (XO) activity and oxidative-stress parameters in human acute paraquat poisoning. Design and methods Twnty-five patients and 26 healthy control participants were recruited. Serum XO, superoxide dismutase (SOD), Glutathione (GSH) and malondialdehyde (MDA) were determined by spectrophotometric methods. Results XO activity and MDA levels were higher and SOD activity and GSH level were lower in the patients group. XO activity and MDA level were significantly higher, and the GSH level and SOD activity were lower in the paraquat poisoning fatality group. There was a significant negative correlation between the XO activity and both the SOD and GSH, while there was a significant positive correlation between XO activity and the MDA level in the patients group. Conclusions XO activity contributes to the development of oxidative injury in patients with paraquat poisoning. Serum XO activity could be used as a marker for prognosis in human acute paraquat intoxication.