In order to determine the insecticidal activity of furan tebufenozide on larvae of the gypsy moth, Lymantria dispar, its toxicity and effects on food utilization and the activities of protective enzymes against the larvae were assayed by “leaf residual film” approach, gravimetric method and measurement of enzyme activities. The results showed that LC50 of furan tebufenozide for 3rd and 5thinstar larvae at 24 hrs was 0.369 and 0.842 mg/L respectively. The duration of larval development was significantly extended, while the larval survivorships were strongly reduced after the 3rdinstar larvae were continuously treated with LC10 and LC30 concentrations of furan tebufenozide. Relative growth rate (RGR), relative consumption rate (RCR), efficiency of the conversion of ingested food (ECI) of the 3rdinstar larvae that fed on Betula platyphylla leaves treated with sublethal concentrations of furan tebufenozide were significantly lower than those of larvae feeding on the untreated Betula platyphylla leaves. After feeding on the Betula platyphylla leaves treated with LC50 dose of furan tebufenozide for 24 hrs, the activities of phenoloxidase (PO), catalase (CAT), and chitinase in the 3rd and 5thinstar larvae and peroxidase (POD) in the 5thinstar larvae showed an “activationinhibitionactivation” response pattern; superoxide dismutase (SOD) in both instars was activated first and then inhibited soon after, whereas peroxidase (POD) in the 3rdinstar larvae was constantly inhibited. The results suggest that furan tebufenozide has a significant insecticidal activity against the L. dispar larvae through its strong impact on larval development, food utilization and enzyme activities.