Abstract: The influences of 18 clones of Populus deltoides on the activities of digestive and protective enzymes in larva o{ Clostera anastomosis were studied. Results indicated that most of the resistant clones inhibited the activities of three digest enzymes in larvae of Clostera anastomosis statistically, while the three digest enzymes activity tested in No. 94-30, 94-12, 74--4 clones were higher than those of controls. The activity of superoxide dismutase (SOD) and catalase (CAT) in larva of Clostera anastomosis were higher than that of control statistically after feeding with resistant clones. However, no distinct effects of No. 94--30, 94--12, 74 4 clones on the activity of the two enzymes, even weak inhibition were showed. A significant relationship between peroxidase (POD) activity in larvae of Clostera anastomosis and certain clones of Populus deltoids did not exist. The results founded scientific basis for selecting new poplar strains worthy of extending in production.