Yogurt and yogurt containing Lactobacillus acidophilus to promote human health, because acidophilus can inhibit intestinal and food-borne pathogens. Diary to evaluate the stability of Lactobacillus acidophilus culture, we examined whether some of the diary lactobacilli can release other dairy lactic acid bacteria bacteriocins phage or inhibited. Purchased two Lactobacillus acidophilus, Lactobacillus 38 strains isolated from 20 yogurt and local food market. Eight Lactobacillus strains as controls. Induced with mitomycin and agar plaque assays, bacteriophages and bacteriocins isolated from these strains and their activities were analyzed. Lactobacillus strains of phage release yogurt 11, while most of the rest from the strain of bacteria hormone release product. A phage, designated Phi Y8, were characterized. It spontaneously Lactobacillus acidophilus Y8 is released from its host About 10 (4) / ml at a rate of at. The phage lysate test strains Lactobacillus nine other dairy products. It has 100 burst size, 39 by elongated prolate head 130 nm, 300nm long flexible but noncontractile tail and linear double-stranded DNA 54.3-kb's. DNA fingerprinting analysis showed that nine of Lactobacillus acidophilus yogurt in this study belong to the same type of phage Phi Y8. Although they may be sensitive to bacteriocins, all phage lysogens resist further attacks, while most nonlysogens respectively two phages and bacteriocins sensitive. Thus, some of the United States yogurt and lactobacillus Lacotbacillus cultures may be unstable or insecure, because they either inhibits bacterial or phage or by their ability to inhibit the release of lactic acid bacteria or other dairy products.