Fermentation is one of the oldest methods practiced by human beings for the transformation of milk into products with an extended shelf-life. The research today focuses on methods of increasing viability of the live cultures, particularly the probiotics, as they are responsible for conferring the health benefits of yogurt. One of the way to improve yogurt both in terms of its potential as a healthy food and as an appetizing product by using Bifidobacterium longum ATCC 15707 this probiotics bacteria effected to reducing symptoms of lactose intolerance, improvement the taste of yogurt and effected on the physical of final product. In this study the measurement the influence of the different ratio between yogurt bacteria and B.longum on the microbial, chemical, physical and sensory characteristics of yogurt product during different storage period. 1% of yogurt starter and 3% of B.longum ATCC15707 decrease significantly yogurt lactose during storage period.