Feeding silkworm breeds on four mulberry leaves varieties had a clear effect  on: 1- Silkgland soluble protein and enzymes: In general, silkworm  breed EM₆ manifested the highest soluble protein and increased GPT activity in the  silkgland, while, the lowest  one was noticed in breed JH₃. In addition, feeding larvae  on leaves of Moritiana and Kokuso-27 increased soluble protein and GPT activity; while, feeding Balady variety decreased soluble protein and  hydrdyzing  enzymes  glutamic pyruvic  transaminase (GPT) and  glutamic ozaloacetic transaminase (GOT). Breed JH₃ manifested the least levels of trehalase, amylase and invertase enzymes activities, while feeding larvae on  other three breeds on leaves of Kokuso-27, Balady and Moritiana varieties increased (in descending  order) the silkgland enzymes, while variety Kanva –2  recorded the  minimum value. 2- Cocoon parameters: Weight of fresh cocoon and cocoon shell weight were significantly affected by both of mulberry varieties and silkworm breeds, as feeding with Kanva-2 variety recorded the highest values. Also silk content ratio of fresh cocoon  was increased in larvae fed on Kanva variety, while it was affected by silkworm breeds. Accordingly, leaves of Kanva-2 variety and breed JH₃ proved to be the most economic in this concern.   3- Silk filament characters: Silkworm breed EM₆ and  mulberry leaves Kanva-2 variety induced the longest of reeled filament and / or the heaviest weight  of silk filament. However, size of silk filament was not affected either with silkworm breeds or mulberry varieties.