This study investigated the influence of four Lactobacillus acidophilus strains (B, V-74, CH-2 and CH-5) and their mixture on the viability of Escherichia coli NCTC 8196 and Staphylococcus aureus NCTC 4163 in fermented milk stored at 7⁰C for 21 days. With no L. acidophilus present, both E. coli and S. aureus remained viable with more than 10⁸ cfu/mL. In the presence of L. acidophilus , no detectable cells of E. coli were recovered after 7 days. Compared to those of its pure culture, the live cell counts of S. aureus were reduced by about 3- to 6-log following 21 days due to the presence of L. acidophilus in the refrigerated fermented milk. The viability loss of E. coli and S. aureus depended strongly upon the strains of L. acidophilus used. L. acidophilus B exhibited the best inhibitory effect o the growth and survival of both cultures tested, followed by L. acidophilus strains CH-2, CH-5 and V-74. The mixtures of four strains of L. acidophilus were more effective in reducing the viability of E. coli and S. aureus than its single-strain cultures. In the presence of L. acidophilus mixed-strain cultures, E. coli generally could not be detected at the starting-point of this storage trial; and the viable cell numbers of S. aureus were less than 20 cfu/mL after 21 days. Use of L. acidophilus as a biological control agent to retard the enteropathogenic bacteria from surviving in dairy products would improve the storage stability of the foods.