The aim of this study was to determine viability in the transit of the Lactobacillus rhamnosus IL1 strain through the stomach and the small intestine. The preservation of the viability of the Lactobacillus rhamnosus IL1 strain in gastrointestinal conditions is one of the main characteristics of the strain, in order to obtain probiotic products. The tests were performed with a cell suspension kept in NaCl 0.5%. The pepsin influence was determined at different pH values, as well as the pancreatin influence in the presence of bile salts. The influence of casein and mucin was also established. The results were read using the ColonyQuant and they were registered in the log (CFU mL-1). Greater viability was preserved in case of mucin which was confirmed by the calculation of the mathematical parameters of viability and mortality, according to whether mucin is used or not. The main conclusion is that the tested strain maintains its viability, even at pH ranging between 1.8-2 and at even greater concentration of bile salts, of 2-3 mg mL-1. These results are confirmed by the cumulated effect of gastric and small intestinal juice, the Lactobacillus rhamnosus IL1 increasing its viability by an average of 20% in the presence of mucin.