The susceptibility of five mango cultivars to the sap sucking insect, Icerya seychellarum was screened and the relation between their susceptibility differences and both leaf nutrients and inhibitors was studied. For this purpose chemical analysis of the leaves of Sultani, Baladi, Hendi, Ewaisi and Alphonso mango cultivars were conducted to estimate their contents of the two main nutritional substances, carbohydrates and proteins, and also their content of two nutrition inhibitors (phenolics and tannins). Based on the obtained results, food quality index (FQI) for each cultivar was calculated. It was found that both the level of susceptibility of mango cvs to I. seychellarum and the values of leaf FQI could be arranged in descending order as follows: Sultani (highly susceptible and had the highest FQI) > Baladi > Hendi = Ewaisi. The results revealed that levels of susceptibility of mango cultivars to I. seychellarum depend on the combined action of leaf nutrients, inhibitors and secondary metabolites which determined the food quality of their leaves. The relative role of these factors may differ among different cultivars.