Fourth instar of silkworm larvae, Bombyx mori L. were fed on mulberry leaves fortified with two different multivitamin sources, natural (bee honey) and synthetic (Pharovit iron). The impact of the larval, cocoon, shell and pupal weight, filament length and weight and the number of breaks during reeling (filament size) were examined. Different results on biological parameters were obtained based on used concentrations or treatments. All the tested concentrations of two multivitamins increased filament size than control except the least concentration of Pharovit iron. Results also established highly significant elevation in the total soluble protein and increased number of protein bands, while decreased significantly the activity of transaminase enzymes (AST and ALT) either in honey or Pharovit treatments comparing to control. Thus, fortification of mulberry leaves with honey enhance protein metabolism, consequently, improving the commercial qualities of filament size, that's very important in sericulture.