Alpha-amylase, pectinase and cellulase are some of the main polysaccharide degrading enzymes in the alimentary canal of the herbivorous insects. In this study, some biochemical characteristics of alpha-amylase, pectinase and cellulase in the larval digestive tract of cotton bollworm, Helicoverpa armigera (Hȕbner) (Lepidoptera; Noctuidae), were conducted using starch, pectin and carboxyl methyl cellulose (CMC) as substrate, respectively. Maximum activity of all three enzymes occurred at pH 9.0 and among different temperatures, the highest activity of enzymes were at 37 ˚C. The effect of different substrate concentrations; 0, 0.25, 0.5, 1, 1.5 and 2 % on the activity of the enzymes was studied. Alpha-Amylase showed optimum activity at 1% starch, activity of pectinase enhanced with increase in pectin concentration, but cellulase activity was not dependent on the concentration of CMC. The effect of some ions as activators or inhibitors was also evaluated. Amylase and cellulase activities significantly declined in the presence of various concentrations of SDS and EDTA, but pectinase activity only diminished by SDS. On the contrary, KCl notably increased pectinase and cellulase activities at 50 mM. In the bioassay, when hexaflumuron (17 ppm) was added to the insect artificial diet, amylase and pectinase activities remarkably decreased as compared to the control in which distilled water was used instead, however cellulase activity was not affected by hexaflumuron (tested by T-test). All assays demonstrated that cellulase activity was significantly lower than amylase and pectinase activities.