ABSTRACTThe aim of the present study was to determine the effects of Bacillus subtilis PB6supplementation on productive performance, egg quality and hatchability of broiler breeder hens. A total of 20,000 broiler breeder hens (ROSS 308), 57 weeks old, were assigned to the two equal groups as follows: The first group was fed a basal diet and the second group was fed the basal diet that supplemented with the Bacillus subtilis PB6(2 × 107cfu/g) at the rate of 1 g/kg of diet. Results indicated that adding Bacillus subtilissignificantly improves egg production (P < 0.05). The body weights and egg weight were not affected by the dietary treatments (P > 0.05) but Bacillus subtilisimproved the egg haugh unit (P < 0.05). Adding Bacillus subtilissignificantly increased hatching egg, eggshell thickness and egg hatchability (P < 0.05). A highly significant improvement was noticed in the faecal score of the group fed with Bacillus subtilis(P < 0.01). Adding Bacillus subtilisincreased the level of total cholesterol (P < 0.01) and decreased the blood heterophil to lymphocyte ratio (P < 0.01) in breeders’ serum. It is concluded that Bacillus subtilis PB6supplementation at the level of 1 g/kg of broiler breeder diet, significantly improve the egg production, egg quality, hatchability, faecal score and return on investment.