This study was carried out to study effect of insect infestation on some internal components of some important cactus plants. So this study was carried out to study effect of insect infestation by three important insects on the internal components of three important cactus plants, Egyption mealybug, Icerya aegyptiaca (Douglas) (Margarodidae: Homoptera) on Aloe vera (Fam. Liliaceae), Agave weevil, Scyphophorus acupunctatus L. (Curculionidae: Coleoptera) on Agave americana (Fam. Agavaceae) and Daphla aphid, Aphis nerii (Boyer) (Aphididae: Homoptera) on Calotropis procera (Fam. Asclepiadaceae). And this study was carried out at two locations (governorates), El-Orman Garden (Giza Governorate) and Antoniadis Garden (Alexandria Governorate) during 2018 season.Results obtained from this study refereed to reduce the concentration of the most internal components of theses cactus plants as result to infestation by these insects. And few internal components its concentration still did not change after infestation by these insects.Statically analysis showed highly significant differences between concentration of the most internal components of the infested cactus plants compared to concentration of the same components in the control (non infested cactus plants).