The purpose of this study was to improve the functional properties of bio-yogurt, which is one of the most popular fermented dairy products widely, consumed worldwide, and to evaluate the effect of whey protein concentrate (WPC) and Arabic Gum (AG) on promoting growth and survival of Bifidobacterium longum. Bio- yogurt was manufactured by using 2% Bifi. longum and enriched with 1% WPC or 2% AG, after milk inoculation by bacterial culture it was incubated at 42±1°C until complete coagulation and then stored at 5±1°C. Chemical, bacteriological analysis and sensory evaluation had been carried out in fresh and after 7 & 14 days of storage. The obtained results indicated that, acid development in control samples without probiotic bacteria or WPC & AG was less compared with Bio-yogurt containing Bifi. longum, WPC and AG, which scored highest acidity and lowest pH values during storage. Moreover, during storage there were an increase in total solids, soluble nitrogen, total nitrogen and acidity and slight decrease in pH values of cheese made with 1% WPC or 2% AG in all treatments. Concerning the bacteriological determinations, there were a slight increase in total bacterial, Streptococci, Lactobacilli and Bifi. longum counts during first 7 days of storage, and then decrease gradually during the second week of storage. In addition, WPC and AG increased the total bacteria, Lactobacilli, Streptococci and Bifi. longum counts comparing with control samples. Generally, the addition of WPC increased organoleptic properties of the product, while the addition of AG did not