Abstract: The effects of sublethal dose of chlorpyrifos (CPF) on food utilization of gypsy moth, Lymantria dispar, as well as CPF toxicity and enzyme activities of carboxylesterase (CarE), glutathione S-transferases (GSTs) and acetylcholinesterase (AChE) were evaluated in the 3rd-instar gypsy moth larvae using gravimetric method and measuring enzyme activities. Relative growth rate (RGR), efficiency of the conversion of ingested food (ECI) and efficiency of the conversion of digested food (ECD) of 3rd-instar larvae fed on poplar leaves treated by sublethal concentration of CPF were significantly lower than those fed on normal polar leaves. However, approximate digestibility (AD) of the treatment was significantly higher than that of control. The relative consumption rate (RCR) of the treatment and control groups were not significantly different. The 24 h LC50 of CPF to the gypsy moth 3rd-instar larvae was 5.86 mg·L-1, which was higher than that of omethoate but lower than that of cyhalothrin. In vitro inhibition assay indicated that the activities of AChE, CarE and GSTs were inhibited by CPF depended on concentrations. The enzyme activity inhibition percent is CarE＞AChE＞GSTs. The results suggest CPF is a kind of effective organophosphorous insecticide for controlling gypsy moth.