The activities of gultathione S transferases (GSTs), carboxylesterase (CarE) and Acetylcholinesterase (AChE) in laboratory strains of the Plutella xylostella have been examined．The result shows that the activity of GSTs of the resistant strain(Cry1Ac–R), Cry1Ac is higher than that of the susceptible strain(Cry1Ac–S). The activities of Care and AChE of the susceptible strain are higher than that of the resistant strain, but there is no obvious difference of detoxification enzymes activity between the two strains. The activities of digestive enzyme of the resistant strain,(Cry1Ac) the susceptible strain and the Bt resistant strain (Bt–T2) have also been examined. The activities of trehalase and sucrase of the susceptible strain are the highest, those of the Bt resistant strain are the lowest, but there is no obvious difference between the two strains in the two digestive enzymes Protesease activity of the susceptible strain of the Plutella xylostella is the highest, while the protesease activity of its resistant strain is the lowest, and the difference of protesease activity between these strains is very obvious.