Abstract: The optimal reaction system of Na+-K+-ATPase from the larval heads of Helicoverpa armigera and Ostrinia furnacalis was set up, respectively. The optimal reaction condition for H. Armigera was 6 μg/mL for protein concentration, temperature 35~40℃ and time 6 min, for O. furnacalis was 8 μg/mL for protein concentration, temperature 35℃ and time 6 min. Under those optimized conditions, effects of α-terthienyl (α-T), a typical photoactivated insecticide, on Na+-K+-ATPase in insect pests were studied. The results showed that Na+-K+-ATPase activity in vivo was significantly inhibited by the near ultraviolet irradiation (300~400 nm), which almost had no effect on that in vitro. However, Na+-K+-ATPase activity in two insect pests after treated by α-T was inhibited both in vivo and in vitro whether irradiation or not. Inhibition rate of Na+-K+-ATPase activity from larvae of O. furnacalis in light group was higher than that in non-light group, and also showing good response-dosage relationship. This suggested that Na+-K+-ATPase might be involved in the mechanism of the action mode of α-T.