Introduction:Different kinds of bacteria,even the same bacteria in different physiological states differ in their structures and chemical components of cell surface.Consequently,under specific conditions,the bacteria can be separated by taking advantage of their difference in cell surface charge.Materials and Methods:Conventional high performance ion exchange chromatography coupled with laser light scattering instrument was employed for the separation and chanracterization of Streptococcus thermophilus (S.t) and Lactobacillus bulgaricus (L.b) for the first time in this paper.