Effect of some growth promoting substances, i.e., yeast extract, fructose, and peptone on the growth rate and acid production by Bifidobacterium bifidum in sterilized skim milk at 40°C was studied. Growth promoting substances were added to milk in three different concentrations, i.e., 0.1, 0.3, and 0.5%. The obtained results indicated that the three substances resulted in an increased of growth and lactic acid production by Bifidobacterium bifidum. The maximum cell population in the presence of yeast extract reached were 25x104, 12x105 and 21x105 CFU/ml after 12 hours. In the presence of 0.1, 0.3 and 0.5%, respectively