The prebiotic potential of fructooligosaccharides derived from native Jerusalem artichoke tubers (JA-Fr) was assessed by monitoring in vitro effects of JA-Fr on bacterial growth. Results showed the greater survivability of beneficial bacteria (lactobacillus acidophilus) in cultures media containing JA-Fr in comparison with HP-inulin (a high molecularweight fraction of chicory-derived inulin). Both JA-Fr and HP-inulin led to a significant increase in bacterial population compared to the control (P<0.05), and the efficacy was proportional to the degree of polymerization (DP). The pH decreased during the lactobacilli activity and no significant differences were observed in the pH with both inulintype fructans. In addition, in vitro evaluation of specific growth rates of Escherichia coli showed that the growth of these bacteria were influenced by the DP and concentration of fructans used in the media.