Toxic effect of dinotefuran, imidacloprid, fenoxycarb, phenthoate and thiocyclam H.O insecticides on greenhouses population of the tomato leafminer,Tuta absoluta (Meyrick) was evaluated in laboratory. Data revealed that the five tested insecticides had high contact toxic effect on moths and 3^rd instar larvae of theinsect. Moths were more susceptible to the effect of tested insecticides than larvae. Imidacloprid was the superior toxicant against moths and larvae, so it had a very low resistance coefficient (RC= 0.01 and 0.13).  Phenthoate and thiocy- clam-H.O. had high toxic effect on two stages. Dinotefuran seemed to have low effect on moths and the same trend was observed with fenoxycarb on larvae. The activity of acetycholinesterase (AChE), glutathione-S-transferase (GST) and monooxygenase (PCMAN-demethylase) was higher in whole body homogenate of untreated moths (1.5, 1.2 and 1.58 times, respectively), than that of 3^rd instar larvae. The exposure of moths and 3^rd instar larvae to LC₃₀, LC₅₀ and LC₈₀ of tested insecticides caused significant reduction (51.11and 25.00%) or increasing (41.78 and 28.77%) in activity of AChE, respectively. Phenthoate treatments reduced AChE activity, but imidacloprid and dinotefuran induced this activity in LC₈₀ treated insects .Low insecticide treatments produced slight induction (1.41-11.90%) of GST, other two treatments produced reduction or increasing enzyme activity of treated insects. LC₈₀   of fenoxycarb had moderate induction (24.79- 27.90%) of moths and larvae GST. A positive correlation between the insecticide concentration and the activity of monooxygenase PCMAN-demethylase was observed in treated insects with five insecticides. Elevation of enzyme activity ranged from 1.59 to 52.12% in moths and 5.83- 59.17% in larvae. Phenthoate and imidacloprid produced the higher induction effect of treated insect enzyme than the other three insecticides.