Olive mill wastewater (OMWW), the main waste product of olive oil extraction process, was investigated as a source of polysaccharides. The yield of alcohol insoluble residue (AIR) was 20.5 % based on the dry matter of OMWW. Extraction with water gave water soluble (WSF) and insoluble (WIF) fractions from AIR with yields of 13.3 % (w/w) and 3.7 % (w/w) based on the dry matter, respectively. Chemical composition and monosaccharide analysis indicated that glucose was the main monosaccharide of these extracts in addition to galactose, arabinose, rhamnose, and galacturonic acid. Prebiotic and antioxidant activities of polysaccharidic fractions from OMWW were evaluated. Results gave evidence for their scavenging capacity toward the 2,2'-diphenyl-1-picrylhydrazyle (DPPH) (IC50 value of 89.43 μg/mL) and hydroxyl radicals (IC50 value of 158.70 μg/mL), resistance toward artificial human gastric juice, and ability to be fermented by Lactobacilli strains.