The antimicrobial activity of Bifidobacterium bifidum and lactis against some pathogenic  bacteria such as Staphylococcus aureus, E. coli and Salmonella typhimurium was investigated during the manufacture and preservation of four types of yoghurt; Traditional yoghurt (TY) (Starter culture), Bifidobifidium yoghurt (BY) (Starter culture + Bifidobacterium bifidum), Bifidolactis yoghurt (LY) (Starter culture + Bifidobacterium lactis) and Mixed yoghurt (MY) (Starter culture + Bifidobacterium bifidum+ lactis). Yoghurt samples were inoculated with 10⁴ cfu/g Staphylococcus aureus, E. coli and Salmonella typhimurium and preserved for 14 days at 4±1^oC. The inoculated bacterial count and the titratable acidity were determined in the prepared yoghurt samples at zero, 3^rd, 5^th, 7^th and 14^th day of storage. The obtained results revealed elevation in the titratable acidity and noticeable inhibition in the count of the inoculated bacteria during the storage period of prepared yoghurt samples at 4±1^oC.