The predator, Cryptolaemus montrouzieri Mulsant, (Coleoptera: Coccinellidae) is an important predator of mealybugs (Hemiptera: Pseudococcidae). It may be fairly, considered a valuable biocontrol agent against mealybugs because other biological control methods proved ineffective due to the waxy coat that covers insect body in addition to its feeding habits. To shed light on the effect of the chemical constituents of a prey on the biology of its predator, certain chemical analyses were carried out on the tested preys to estimate the protein, carbohydrate, lipids, sodium, potassium, and calcium contents. The present work dealt with the host preference of the predator, C. montrouzieri by using chemical analysis of certain constituents (protein, carbohydrates, lipids, calcium, sodium together with the Potassium) of Planococcus citri (Risso) (Hemiptera : Pseudococcidae) eggs, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs and Schizaphis graminum (Rondani) ( Hemiptera: Aphididae) nymphs. Chemical analysis of certain constituents of the tested preys of the predator C. montrouzieri showed that P. citri eggs had the highest total carbohydrates (31.37mg/g), total lipids (8.81 mg/g) and potassium content (1.3179 /mg), compared to the other two prey species ( E. kuhniella eggs and S. graminum nymphs). It could be finally concluded that the greatest constituents of carbohydrates, lipids and potassium in eggs of P. citri are mostly, the reason of its suitability for rearing the predator C. montrouzieri.