Enteric flora constitutes 95% of the cells in the human body. It has been shown that the bacterial content of this flora is affected by diet and changes in nutrition. Considering that urinary tract infections (UTI) are mostly due to ascending infections from the gut flora, the importance of the elements of this flora and their characteristics becomes more evident. The aim of this study was to evaluate the influence of oral Saccharomyces boulardii (S. boulardii) intake on the number of Escherichia coli (E. coli) colonies in the colon. This study was carried out with 14 boys and 10 girls (total of 24 children) aged between 36 and 192 months (mean: 104.3+/-45.1 months). A commercial capsule or powder containing 5 billion colony-forming units (cfu) of S. boulardii was administered once a day for 5 days. The number of E. coli and yeast colonies was measured in the stool samples of the study group before and after the use of this drug. Before treatment, the mean number of E. coli colonies in g/ml stool was 384,625+/-445,744. This number decreased significantly to 6,283+/-20,283 after treatment (p=0.00). S. boulardii was not detected in stool before treatment and the number of colonies increased to 11,047+/-26,754 in g/ml stool. S. boulardii may be effective in reducing the number of E. coli colonies in stool. The influence of this finding on clinical practice such as prevention of UTI needs to be clarified by further studies.