The effects of the juvenile hormone analogues pyriproxyfen [2-(1-methyl 1-2-(phenoxyphenoxy) ethoxy) pyridine] on total protein, amino acid tranferases, acid and alkaline phosphatases of Spodoptera littoralis were studied after feeding the 4 ^th and 6 ^th instar larvae on the LC ₅₀ (225 ppm) of the tested compounds. The results showed that pyriproxyfen caused a significant reduction in the level of the total protein at all time intervals tested (48, 72, 96 and 144 hours). The data revealed that there was a significant increase in activity of glutamatic Oxaloacetic transaminase (GOT) during the different time intervals comparing with the untreated check. While there was a significant reduction in the level of glutamatic pyruvic transaminase (GPT) after 48 and 72 hours in both 4 ^th and 6 ^th instar larvae. In contrast, at 96 and 144 hours, there was a significant increase. Pyriproxyfen also cause a significant decrease in activity of alkaline phosphatase (alkapase) and acid phosphatase at different time intervals.