Abstract: Kinetics of xylooligosaccharides(XOS) metabolized by Bifidobacterium adolescentis was investigated, and the components of XOS and the main metabolites were analyzed during the metabolism. The results showed that total sugar concentration decreased from 5.00 g/L to 3.59 g/L when XOS was used as sole carbon sources for B. adolescentis after 48 h metabolism in vitro, cell concentration increased from 0.10 g/L to 0.35 g/L and the pH value decreased from 7.00 to 4.75. Xylobiose to xylopentaose were metabolized by B. adolescentis firstly when XOS was used as carbon sources, after that, arabinose was released from arabinosyl groups in XOS mixture by α-L-arabinofuranosidases from B. adolescentis during the metabolism, and then arabinose was metabolized ultimately. Free xylose was accumulated by releasing from the end chain of XOS by β-D-xylosidase from B. adolescentis. The main metabolites were lactate, acetate, propionate and butyrate.