Xylooligosaccharides (XOS) are polymers of the sugar xylose bound by β(1→4) glycoside bonds. XOS have potency as a prebiotic and can be produced from agricultural waste such as cassava dregs. The purpose of this study was to examine prebiotic potential of XOS derived from cassava dregs from hydrolysis reaction catalyzed by endo-β-1,4-D-xylanase. The prebiotic activity of XOS derived from cassava dregs was examined by the number of Bifidobacterium, Lactobacillus, and Escherichia coli in Balb/c mice colon, the fermentation products of Bifidobacterium and Lactobacillus including changes in pH in the colon and short chain fatty acids (SCFAs) produced by the bacteria as well as the concentration of Ca²⁺ excreted through mice faeces. This study administered XOS derived from cassava dregs at 0.5 and 1.0 g (kg.BW) for 14, 21, and 28 days. The negative control group was Balb/c mice without XOS derived from cassava dregs. The results showed that feeding with XOS derived from cassava dregs at 0.5 and 1.0 g/(kg.BW) could increase the number of both Bifidobacterium and Lactobacillus and decrease the number of E.scherichia coli. The main fermentation products of Bifidobacterium and Lactobacillus were SCFAs such as acetic acid and butyric acid with respective concentrations of 11.57 and 2.97 mM. The pH in the colon of treatment groups was more acidic than that of in the control groups. The Ca²⁺ absorption was increased by 0.27% (w/v) that is characterized by decreased concentration of Ca²⁺ in Balb/c mice faeces of treatment groups. This study has led to a conclusion that XOS derived from cassava dregs of xylan hydrolyzed by endo-β-1,4-D-xylanase has prebiotic effect.