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Two strains of Lactobacillus acidophilus and Bifidobacterium infantis isolated from breast-fed infants stool were tested to determine their suitability for use as probiotics by conducting a special protocol. The protocol includes the following tests: acid tolerance, bile tolerance, cholesterol assimilation, adhesion to the digestive system test and the test of their viability in the feed. Both isolates showed good acid resistance at pH of as low as 2, although the viable count was significantly decreased (p< 0.5) from 7.65±0.07 and 8.15±0.05 at zero time to 7.22±0.01 and 6.15±0.21 after 60 minutes for L. acidophilus and B. infantis, respectively. The isolates could tolerate bile salt of 0.3% concentration, although the viable counts decreased significantly (p< 0.5) from 8.91±0.03 and 9.52±0.04 on 0% bile salt to 8.59±0.01 and 8.69±0.02 on 0.3% bile salt for L. acidophilus and B. infantis, respectively. Assimilated cholesterol was significantly higher (p< 0.5) for L. acidophilus (76.0%±3.5) as compared with B. infantis (57.7%±2.1). Both could adhere to rat intestine as the viable counts of third washing were 6.82±0.05 and 7.85±0.02 for L. acidophilus and B. infantis, respectively, as compared with the control (3.57±0.04). Also, both isolates could stay viable in the rat diet, with the minimum acceptable level, for 2-3 days. On the basis of the results of this study, it can be concluded that both isolates have the characteristics of probiotics strains.