The isolation of a novel endophyte Pantoea ananatis, a bacterial leaf blight on mulberry leaves is the first record in Egypt. Four bacterial isolates (L1, L2, L4, and L5) were obtained from infected and healthy mulberry leaves and were identified by classical techniques which exhibited short rods and Gram-negative as well as their biochemical and physiological characteristics. Molecular identified rDNA sequences of four isolates were performed. The phylogenetic tree analysis confirmed that all isolates belong to P. ananatis. After the pathogenicity test on leaves, bacterial isolates L1 and L4 produced a typical symptom on mulberry leaves. Larvae of mulberry silkworm, Bombyx mori were orally infected with each of the four P. ananatis isolates separately to assess the silkworms' immune response. Significant variation was observed in the protein concentration and the appearance of the new hemolymph protein bands profile in the infected larvae. It is interesting to note that the immunized hemolymph of the infected larvae exhibited a marked increase in the quantity of antimicrobial peptides with molecular weights less than 30 KDa and the intensity of major proteins. However, the total protein count and humoral immune showed that the bacterial isolates L2 and L5 were more pathogenic to B. mori.