The monosaccharide composition and the structure of polysaccharide from Pichia fermentans were analyzed. The yeast cells were broken with ultrasonic disruption and the crude polysaccharide was precipitated by addition of ethanol. Then, the crude polysaccharide was separated by diethylaminoethyl(DEAE) cellulose column separation and an acquisition of uniform water-soluble polysaccharide yeast polysaccharides 5(YP5) was obtained. The results of gas chromatographic analysis indicated that the glycosyl was made of rhamnose, arabinose, xylose, mannose, glucose and galactose, whose molar ratio was 9.51∶ 1.33∶ 2.31∶ 0.94∶ 84.93∶0.96, respectively. The molecular weight of polysaccharides YP5 was 8.3×10~4 measured by Ubbelohde viscosity method. Combination of IR and ~1H NMR analysis showed that the YP5 owned characteristic infrared absorption peaks of polysaccharide and contained amino groups. The β-D-glucan was main glucosidic linkage of polysaccharides PY5.