Activity and some properties of Helicoverpa armigera Hübner and Spodoptera exigua Hübner (Lep.: Noctuidae) midgut proteaseAbstract : In this study some properties of Cotton bollworm and Beet army worm midgut protease activity was investigated. Insects were reared on special artificial diets in controlled conditions. Different developmental stages including, larval stages, 5-6 inter-moult period, pre-pupa, male and female pupa and adult?s protease activity measured using azocaseionolytic assay method. Optimum pH and temperature of protease activity determined by testing different pH and temperature gradients. Also protease stability in two different storage conditions (4 and -20 °C) for 15 weeks were studied. Results showed that the optimum temperature for protease activity was 35°C in both insects. Studying the effects of different pH values on protease activity in both insects showed that except pH 13, enzyme activities were not affected by acid or alkaline conditions. Specific protease activity in 4th larval stages of both studied insects was more than other developmental stages. Protease activity in male and female pupa and adults of S. exigua was not significantly different, but in H. armigera male pupa and female adults have significantly more protease activity than other related sexes.