Abstract: To clarify the biochemical mechanism of phosphine toxicology, studies were undertaken to establish the effects of phosphine fumigation on the mortality and oxidative metabolism in 3rd instars of Bactrocera dorsalis Hendel. under 25℃. The results showed that: (1) the dosages to achieve 50%, 90% and 99% mortality were 0.28, 0.37, 0.46 mg/L respectively in 48 h fumigation at 25℃; (2) the respiration of B. dorsalis was consistently inhibited during the fumigation; (3) phosphine inhibited catalase activity with maximum inhibition rate 55.99%, increased peroxidase and superoxide dismutase activity and inhibition of hydroxyl radical capacity with the greatest increasing rates of 141.48%, 130.21%, 155.90% respectively. These results confirmed the toxicity of phosphine against B. dorsalis, and verified that accumulation of reactive oxygen species was one possible mechanism of phosphine toxicology by inhibiting the activity of catalase.