The role of detoxifying enzymes, mixed function oxidases (MFO's), and carboxyl ester hydrolase (CEH) was studied in the resistant populations of diamondback moth Plutella xylostella L collected from Coimbatore region where indiscriminative use of new insecticides were surveyed during the study period 2010-2013. The enzyme activity of two enzymes was measured in terms of specific activity (n moles min-1 mg protein-1). The enzyme activity of MFO was increased over control to the extent of 32.52 and 28.68; 28.11 and 32.25; 22.37 and 40.08 and 34.48 and 44.49 per cent in third and fourth instar larvae treated with chlorantraniliprole 18.5 SC, spinosad 2.5 SC, emamectin benzoate and quinalphos 25 EC respectively, after 18 hours after application. The specific activity of CEH, 24 hours after application of emamectin benzoate 5 SG showed an increase of 10.15 per cent in the third insar larvae. No such induction of enzyme was noticed with chlorantraniliprole 18.5 SC, spinosad 2.5 SC and quinalphos 25 EC. These results suggested that, diamondback moth might have high risk of developing resistance to chlorantraniliprole 18.5 SC, carboxylesterase and mixed function oxidase might be involved in the resistance of the DBM to chlorantraniliprole 18.5 SC. However, from the induction of CEH enzyme in the larvae treated with emamectin benzoate 5 SG alone in the present study indicated by the marginal increase in carboxylesterase activity, hence its importance in detoxification of the newer insecticides cannot be totally ruled out.