In the past two decade, the application of probiotics to the inhibition of pathogenic or microorganisms has recieved much interest. The aim of the present was to study the effect of Bifidobacterium angulatum, Bifidobacterium bifidum, Lactobacillus acidophilus and Lactobacillus casei on Escherichia coli O157:H7 was evaluated during associated growth in milk. At first a quantity of 1. 5×108 E. coli O157:H7 was inoculated to 500 ml of sterilized milk, homogenized and distributed equally in five erlene meyers. The first erlene meyer was considered as the control one and into the second, third, fourth and fifth a quantity of 1. 5×108 of the above probiotics were inoculated, respectively. after 24 and 48 hours of incubation at 37 °C, pH and the number of E. coli per ml of them were determined using pH meter and pour plate method in VRBA medium. This procedure was repeated 10 times and the mean of pH and number of E. coli per ml of the Control and probiotic treatments was compared by one way ANOVA Results showed that associated growth of mentioned probiotics significantly (p<0.01) inhibited the growth rate of E. coli O157:H7 during 48 hours incubation. The pH of sample containing E. coli + L. Casei was lower than the control after 48 hours incubation (p<0.01). It can be concluded that the consumption of products containing mentioned probiotics could have beneficial effects on prevention and treatment of E. coli O157:H7 contamination.