This study was conducted to evaluate the toxicity and biological effects of ethanolic leaf extract of Simmondsia chinensis on 2^nd and 4^th instar larvae of cotton leafworm, Spodoptera littoralis, as well as the effect on total protein content and the activity some enzymes of S. littoralis larvae after 48 and 72 hr of treatment. The obtained results indicated that the extract was more effective on the second instar larvae than the fourth one.  The LC₅₀  of the jojoba extract on the 2^nd instar larvae was less than that on the 4^th instar larvae , as well as it was decreased by increasing the period after treatment indicated that the larval mortality was higher on 2^nd     instars than 4^th  ones. Larval duration was shortened at all treatments of the 2^nd instars compared with control. Pupae mortality was high on the 2^nd instar treatments comparing with that of the 4^th instars, also, the pupae duration was shortened at all treatments of the 2^nd and 4^th instars compared with control. The percentages of emerged moths were decreased by increasing the extract concentrations.There were significant differences in the egg laid per female between treatments and control. Total protein after 48 hr. of treating was decreased from 32 mg/ g b wt. in control to 31.8 mg/ g b wt. at treated larvae with – 0.36 % change, while it was 19.5 mg/g b wt. at control compared to 14 mg/ g b wt. after 72 hr. with –28.21 % change. As for the enzymes activity it was observed that nearly all enzyme activities were decreased in comparison with control except α-esterase activity which was decreased to 15.3µg-a-naphthal/min/mg protein after 48 hr. from treatment compared with control 27.7 µg-a-naphthal/min/mg protein and increased to 23.2 µg-a-naphthal/min/mg proteinafter72 hr. from treatment compared with control 19.5 µg-a-naphthal/min/mg protein. Also, AkP activity which increased to 20.5 U x 10³/mg protein after 48hr. of treatment, compared with control7.9 U x 10³/mg protein and decreased to 3.7U x 10³/mg protein compared with control 5.8 U x 10³/mg protein after72 hr. of treatment. Jojoba is suggested as a safe product with a potential for use as a bioinsecticide in integrated pest management especially in urban localities where use of chemical insecticides are discouraged.