AbstractXylooligosaccharides (XOS) obtained by autohydrolysis of rice husks were demonstrated in a previous study to act as fermentable substrates by the intestinal microbiota in human fecal slurry cultures, leading to the generation of acetic and lactic acids and supporting the growth of bifidobacteria (Gullón et al. 2011). The purpose of the present study was to provide new insights into other possible targets of XOS action by determining (in the same fecal cultures) the levels of some relevant intestinal microbial groups and the profile of Bifidobacterium species by quantitative and qualitative polymerase chain reaction (PCR), respectively. XOS-containing concentrates promoted the growth of Lactobacillus-Weissella, Bacteroides-Prevotella, and Clostridium cluster XIVa groups, as well as Faecalibacterium prausnitzii species. Preliminary results point to possible variation in the profile of some bifidobacteria species in fecal cultures caused by XOS that should be further investigated. These results support XOS as potential prebiotics for the design of functional food products.