Recently the tomato leafminer, Tuta absoluta become one of the most devastating pests of tomato in Egypt. Chemical control has been the main method of controlling it. To select the best insecticide for control this insect, susceptibility tests were made under laboratory conditions. Nine insecticides were tested against field T. absoluta 2^nd instar larvae. Imidacloprid and Thiocyclam-H.O. were the most powerful insecticides and the insect had no resistance to them. Lufenuron, Dinotefuran, Fenoxycarb, Diflubenzuron and Phenthoate gave moderate toxic effect and resistance level except Phenthoate and Fenoxycarb. The two bio-insecticides had the lowest effect on larvae with low level of resistance, but Bacillus thuringiensis kurstaki is more toxic than Nuclear Polyhedrosis Virus (NPV). Treatment of T absoluta 2^nd instar larvae with LC₅₀ of tested insecticides decrease the total protein content in the whole body homogenate of treated larvae compared with that of control insects. A significant depletion of protein concentration presented in Phenthoate (-46.8%), Imidacloprid (-43.0%) and Dinotefuran (-39.1%) treatments. LC₅₀ treatment of tested insecticides elevated the activity of Cytochrom P450 (PCMAN-demethylase monooxygenase)and Superoxide dismutase (SOD) enzymes in tissues of treated larvae than control. The highest significant increase in PCMAN-demethylase monooxygenase activity (157.1%) was detected in tissues of Phenthoate larvae. The more pronounce increasing in (SOD) activity was observed in Imidacloprid larvae.  Fractionation of the total protein contents in whole body homogenate of T. absoluta larvae on SDS-PAGE revealed that the depletion of protein concentration correlated to disappearance of several proteins and reduction of bands intensity in treated larvae compared with control. The highest difference in protein pattern (37%) presence between control and  treated larvae with Phenthoate , Imidacloprid and Dinotefuran. The aforementioned results revealed that the all tested insecticides had toxic effect on the tomato leafminer and caused biochemical disturbance in their bodies. So that, we can be use small amount from the effective chemical insecticides in rotation with IGRs and bio-insecticides in integrated pest management (IPM) program of this pest.