The digestion of xylobiose was investigated in vitro. Xylobiose was not hydrolyzed by saliva, pancreatin, gastric juice or intestinal mucosa homogenate. The fate of xylobiose was studied after oral administration. The xylobiose ingested was not excreted into feces and urine during 24h after administration. These results suggest that xylobiose is utilized in vivo not by the action of digestive enzymes but by the action of the intestinal flora.