Two different Thai hybrids (1 and 2) of mulberry silkworm, Bombyx mori L. were reared under the Egyptian climatic conditions. The fitness of imported hybrids was compared with Egyptian hybrid (as a control) in different aspects. Biological parameters viz; egg hatching percentages, larval weight, Effective Rate of Rearing (ERR), cocooning and pupation percentages, pupal weight and egg fertility were recorded. Economical parameters viz; cocoon, cocoon shell weights and cocoon shell ratio, as well as, technological parameters viz; filament length, weight, size and silk percentage were studied. Mature larval haemolymph total proteins, free amino acids, protease and transaminases (GOT and GPT) enzymes were measured colorimetrically. Imported hybrids were significantly higher than the local in most of the tested parameters. Hybrid 1 recorded a significant increase in: larval wt, cocoon shell %, randitta, as well as, filament length, size and silk percentage. While Hybrid 2 was significantly higher in hatching and pupation percentages. Haemolymph total proteins and free amino acids were significantly high in both hybrids 1 and 2 compared with local one. The same trend was observed for tested protease and transaminases enzyme activities. It may be recommended to use these two imported hybrids in the breeding programs as parents for the production of superior local hybrids.