© 2016 Japan Society for Bioscience, Biotechnology, and Agrochemistry. Water-soluble sulfated heteropolysaccharides were extracted from Cladophora glomerata Kützing and fractionated by ion-exchange chromatography, which yielded two subfractions, F 1 and F 2 . The crude and fractionated polysaccharides (F 1 and F 2 ) mostly consisted of carbohydrates (62.8-74.5%) with various amounts of proteins (9.00-17.3%) and sulfates (16.5-23.5%), including different levels of arabinose (41.7-54.4%), galactose (13.5-39.0%), glucose (0.80-10.6%), xylose (6.84-13.4%), and rhamnose (0.20-2.83%). Based on the size exclusion chromatography (SEC) profiles, the crude and fractions mainly contained one peak with shoulders having molecular weight (M w ) ranges of 358-1,501 × 10 3 . The F 1 fraction stimulated RAW264.7 cells to produce considerable amounts of nitric oxide and cytokines compared to the crude and F 2 fraction. The backbone of the most potent immunostimulating fraction (F 1 ) was α-(1→4)-L-arabinopy-ranoside with galactose and xylose residues as branches at O-2 position, and sulfates mainly at O-2 position as well.