The purpose of this study was to test the viability of the probiotic bacteria product in a unicameral system, gastrointenstinal simulation (GIS1), for in vitro simulation of the conditions in the stomach and small intestine. The product contained a ratio of 1:1 Lactobacillus paracasei YR and Enterococcus faecium VL47 strains, in freeze-dried form and 10 g/L lactulose. The strains’ viability was evaluated under simulated gastric and small intestine conditions, in comparison with Lactobacillus johnsonii La1 strain. The experiment was performed in the presence/absence of lactulose. The strains of L. johnsonii La1 and E. faecium VL47 have shown a better resistance to bile salts and low pH, in comparison with L. paracasei YR. The survival capacity, Cs, was equal to 0 for L. paracasei YR after addition of pancreatic juice and bile salts. Losses for the other 2 strains were about 6 log CFU/mL after transit through the compartments.