The fall armyworm, Spodoptera frugiperda (J.E Smith) (Lepidoptera: Noctuidae), causes direct damage by feeding on many crops. parts of the host plant. The aim of the study is to estimate the effect of Bacillus thuringeinsis var. kurstaki on S. frugiperda. Our results indicate that the value of LC₅₀ was 0.125 mg/ml. Treatment of second instar larvae of S. frugiperda by LC₅₀ of B. thuringeinsis kurstaki caused a prolongation of larval duration and pupal duration, and a significant reduction in pupation%. The biochemical studies on 6^th instar larvae of S. frugiperda after treatment as 2^nd instars by LC₅₀ of B. thuringeinsis kurstaki showed a significant decrease in the activity of Amylase enzyme and Trehalase compared to untreated larvae, while Invertase activity was significantly increased compared to control. The results showed a general disturbance in three carbohydrate enzymes in larvae treated as 2^nd instars of S. frugiperda with LC₅₀ of B. thuringeinsis kurstaki.