The antidiabetic function of polysaccharides prepared from six legumes: soybean, white kidney bean, red kidney bean, small black soybean, field bean, lentil were studied. Six legume polysaccharides' antidiabetic function in high-fat diet and streptozotocin-induced type II diabetic mice were compared. Their effects on body weight, fasting blood glucose (FBG), glycosylated serum protein (GSP), serum insulin levels (HOMA-IR), blood lipids (including total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-c), and high-density lipoprotein cholesterol (HDL-c)) were tested. Results showed that red kidney bean polysaccharides (RK) could alleviate the symptoms of emaciation, decreased the levels of FBG, GSP, TC, LDL-c and obviously reduced the concentration of TG and HOMA-IR (p < 0.05). RK exhibited greater antidiabetic potential in type II diabetic mice, compared with other legume polysaccharides. The chemical composition of six legume polysaccharides were determined. Composition analysis indicated that the six legume polysaccharides were obviously different in moisture, ash, neutral sugar, uronic acid, total phenolic content, total flavonoid content, amino acid composition and monosaccharide composition. Results indicated that the antidiabetic activities of RK might due to its higher content and specific structure of polysaccharide.