Terfezia arenaria, desert truffle harvested from the Algerian Sahara, is traditionally known by its particular nutritional values and its important healthy benefits. Through determination of chemical composition, phagocytic activity and α-glucosidase inhibitory activity of water-soluble polysaccharides was revealed. T. arenaria ascocarps contain 28% total carbohydrate, 4% crude fiber, 24.9% total proteins, 9.65% ashes (266.7ppm of Sodium, 4633.33ppm of Potassium), 3.83% lipids, 1.13 % total polyphenols, 0.6% free sugars and 0.23% flavonoids. Water-soluble polysaccharides (WSP) were extracted from T. arenaria ascocarps by the sequential use of hot-water extraction, ethanol precipitation, ultra-filtration, and anion-exchange chromatography, which afforded a yield of 9.42%. The chemical composition of WSP was mainly consisted of 60.11±2.28% carbohydrates, among them 97.4±2.26% are neutral monosaccharides and 03.22±0.11% are uronic acids, and 17.27± 1.48% proteins. Analysis of monosaccharides by gas chromatography (GC/MS) indicated that the majority component was glucose. In order to evaluate the immunostimulatory effect of WSP, phagocytic activity of opsonized human leucocytes against opportunist pathogen yeast, Candida Albicans, was assessed. Compared with the control, WSP could significantly (p < 0.05) enhance phagocytic capacity at the dose of 1 mg.ml-1, which showed a phagocytic activity of 9.33%. Moreover, the hypoglycemic activity of extract was determined by α-glucosidase inhibitory activity, in vitro. WSP displays a promising inhibitory activity with an IC50 value of 71.96 mg.ml-1, significantly lower than that of the well-known synthetic α-glucosidase inhibitor, acarbose, which had an IC50 value of 9.62 mg.ml-1. The results of this work provide new knowledge in the field of chemical composition and biological activities of polysaccharides of Terfezia arenaria ascocarps and might play an important role in activating phagocytosis leucocytes cells, thus having contribution to antidiabetic activity.