Four strains of  bifidobacteria ( Bifidobacterium angulatum  ATCC 2238, Bifidobacterium animalis subsp lactis Bb12 , Bifidobacterium bifidum ATCC 2203, and Bifidobacterium bifidum  LMG 10645) were studied  for acid tolerance and growth in different types of mammalian milks . All studied strains grew at a wide range of pH , ranging from pH 2.0 - pH  6.5 .  However the growth was quite low at pH 2.0 , it was in the range  between (0.07 - 0.12  optical density at 660 nm  ) and slightly higher when the pH of the medium was raised to pH 3.0 , at this pH  the growth was between ( 0.08 - 0.18) optical density at 660 nm    . On the other hand , at pH 4.0   the optical density was ranging between ( 0.90 - 2.10  at 660 nm)   . The higher growth rate was achieved at pH 6.5 , it was between (3.55- 4.35) optical density at 660 nm. The studied strains were grown in human, cow,  goat, buffalo, sheep and camel milks. All strains were able to grow at  the six types of milk , the growth was in the range between 1.5 x10⁶ cfu /ml (sheep milk ) -  2.1x10⁷ cfu /ml (cow milk ) a slight decrease was noticed when Bifidobacterium angulatum 2238  was grown in sheep milk . Bifidobacterium bifidum 2203 reached the count of 10 x10⁹ cfu /ml in goat milk and the lowest growth was noticed in human milk .  The slowest growth of Bifidobacterium animalis subsp lactis Bb12 was 7.5 x10⁵ cfu /ml , it was found when it was grown in camel milk  and  the best growth was noticed in  goat and sheep milks . Bifidobacterium bifidum  LMG 10645 grew well in all types of milk except human milk , the growth rate was almost around 10⁶ - 10⁷  cfu /ml,whereas a slight decrease was noticed when they grew in human milk 5.9 x10⁶ cfu /ml.