[Objectives]  To clarify the metabolic mechanisms underlying the resistance of Plutella xylostella (L.) to spinetoram. [Methods]  The activity of glutathione-S-transferase, carboxylesterase and acetylcholinesterase and multifunctional oxidase were measured using the enzyme kinetic method in a highly resistant, moderately resistant and a susceptible strain of P. xylostella. [Results]  The specific enzyme activities of glutathione-S-transfer enzyme, acetylcholinesterase and carboxylesterase were significantly higher in the highly resistant strain than in the susceptible strain. Specific activity to these insecticides were, respectively, 15.38, 3.15 and 7.30 OD·min^-1·mg^-1pro in the highly resistant strain. There was, however, no significant difference in acetylcholinesterase activity between the moderately resistant and susceptible strains, or in multifunctional oxidase activity among all three strains. The specific enzyme activity of multifunctional oxidase activity was 4.97 in the highly resistant strain、4.08 in the middle resistant strain, and 4.23 OD·min^-1·mg^-1pro in the susceptible strain, respectively. [Conclusion]  The glutathione-S-transferase, carboxylesterase, and acetylcholinesterase, activity increased with the level of resistance. There was no significant difference in multifunctional oxidase activity among the three strains. Further investigation of the metabolic mechanism underlying spinetoram resistance in P. xylostella should therefore focus on glutathione-S-transferase, carboxylesterase, and acetylcholinesterase.