This research was conducted in the laboratories of Faculty of Agriculture – Damascus University Department of Food Sciences. The aim of this research was to study the inhibition effect of the growth and activity of Lactic acid bacteria as starter in yoghourt, on the growth of E. coli O157:H7 bacteria. A pure strains of E. coli O157:H7 and Lactic acid bacteria was used for this study. The effect of Lactic acid bacteria (Streptococcus thermophilus and Lactobacillus bulgaricus ) in the number of E. coli O157:H7 was studied in 37 ◦C and 4◦C. The Lactic acid bacteria was inoculeted in milk which was prepared to manufacture the yoghurt. The number of E. coli O157:H7 was gradually decreased with the time. The decline number of this bacteria was clear when S. thermophilus and Lb. bulgaricus were used as a mixture starter , then when Lb. bulgaricus was used as a single starter then S. thermophilus was used a single, In the other hand, the inhibition effect was weaker at 37 C and stronger on 4 C.