Two lots of yogurt were prepared to contain two different strains of Yersinia enterocolitica (E675 serotype 0:3 and 2653 serotype 0:8) at an initial inoculum of 2 × 106 cells/ml, and then were refrigerated at 5±1°C for 7 d. Numbers of Y. enterocolitica, as well as pH value of yogurt were determined every 24 h. Y. enterocolitica survived until the end of the week at a population of 8,000 and 10,000 cells/ml for each strain, respectively. The pH value of yogurt decreased sharply from 6.3 to 4.5 by the end of preparation, and a low value of 4.2 was reached at the end of refrigerated storage.