Background: Metabolic capacity of gut microflora is huge and this “microb” organ can be considered as second biggest metabolic organ in body. The potential for an antibiotic to influence gut microflora is related to its spectrum of activity, pharmacokinetics, dosage and length of administration. In terms of pharmacokinetics, the rate of intestinal absorption plays a fundamental role. Apart from basic physiological functions, bile acids and their analogues are recognized as transport promoters for other substances, in potentiating their action. The aim of this study was to demonstrate potential protective effect of monoketocholic bile acid on rat intestinal microflora from oral ampicillin.