The silkworm is an important economic insect due to production of silk. It is the larva or caterpillar of the domesticated silk moth, (Bombyxmori L.) . In the rearing of silkworm bacterial flacherie considered the most important disease effect in silk production. Flacherie is a Syndrome associated with bacterial disease. In the present study the isolation of pathogenic bacteria from infected larvae . The infected larvae samples were serially diluted from which 10-5,10-6 and cultivated onto nutrient agar plate. The dominant colonies were selected identification by colony morphology, Gram staining property and biochemical test and confirmed the identification by 16SrRNA which proved the name of bacteria as Bacillus thuringensis SW2 with accession number (MK327364.1). The genus of Bacillus thuringensisSW2 was responsible of mortality in 4th and 5th instars of the larval stages of B. mori L. after 3 days recorded 4.66a and 2.66b in 4th, 5th instars respectively post infection and highest mortality rate was obtained at 5 days recorded 12a, 12.66a in 4th and 5thinstars receptively and the total injury reach to 31a,32a in 4th and 5thinstars receptively after 5days.