The ultrastructure, protein and Protein patterns of fat bodies ill three Insects(Pieris rapae, Lucillia illustris, Acrida cinerea) at various developmental stages have been investigated by means of electron microscope, Biuret method and acrylamide gel electroph-oresis. 1. The number of glycogen particles reached maximum before moulting, decreased at mid stages and restored in adult. 2. The concentration of lipid droplets reached maximum at late pupa in Pieris rapae, at prepupa in Lucillia illustris and at last instar in Acrida cinerea. 3. Protein concentration changed significantly throughout the larval-pupal-adult transformations and patterns also were specific for each stage. 4. A total of 24 bands in Pieris rapae, 28 in Lucillia illustris, and 30 in Acrida cinerea were identified, respectively. 5. Histochemical staining of the arcylamide gels by the PAS method, toluidine blue and Sudan black demostrated that the carbohydrate, mucopolysaccharide and lipid were associated with certain fat body proteins, and several esterase and phosphatase bands were found. too.