It is important to understand the effects of increasing temperatures due to global warming on Egyptian cotton leafworm Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) which damages a wide variety of crops in the Middle East and is one of the major economic pests of cotton in Egypt. Therefore,we are investigating five different constant temperatures at 15, 20, 25, 30and 35^oC as different thermal effects on biochemical parameters and enzymes of fourth larval instars. Biochemical analyses were performed to determine the effects of these different constant temperatures on the amount of total proteins, lipids, carbohydrates and free amino acids as well as metabolic, digestive, neural and detoxification enzymes. It's clear from the results that the total amount of proteins, free amino acids as well as, the activity levels of proteases were increased significantly by raising of temperatures to reach their maximum activities at 30^oC. While the total amount of lipids, Carbohydrates  were decreased significantly by raising of temperatures. Moreover, activity levels of amylase, invertase and Trehalase were decreased at 15^oC.Amylase and invertase reached their maximum activity at 30^oC,while Trehalase reached its maximum activity at 20^oC. There was severe reduction in carbohydrate enzymes activities at 35^oC. On other hands, the activity levels of total lipids and lipase were increased significantly at lower temperatures 15^oC and 20^oC, no significant changes were detected between other temperatures. The activity levels of GOT and GPT increased significantly and reached their maximum level at 20^oC.However, GOT and GPT at other temperature were significantly different. The level of GST Enzyme was increased significantly at 30^oC, while, its activity level was decreased at 15^oC.  Moreover, AchE, Alpha (EST-α) and beta esterase(EST-β) enzymes were increased gradually at 15,20 and 25 ^oC. They reached their maximum activities at 25^oC followed by the reduction in activity levels at 30^oC and 35^oC.