The present study was performed in order to evaluate the biological and biochemical effects of commercially formulated Bacillus thuringiensis kurstaki (BTK) and a locally isolated BTK against the cotton leafworm, Spodoptera littoralis, under laboratory conditions. Two commercial bioinsecticides; Protecto^® and Dipel DF^®, and the local isolated B. thuringiensis kurstaki (BTK) were tested against 2^nd and 4^th instar larvae of S. littoralis. The results showed a decrease in both mean larval and pupal duration of the larvae, which were treated as 2^nd and 4^th instar larvae. The results also showed a decrease in the rate pupation and the adult emergence percentage compared to the control. The results also showed influenced by the mean adult longevity for both male and female moths as a result of treatment with studied compounds. In addition, results showed that the treatment with tested bioagents led to a negative impact on the activity of certain enzymes.