In this study, the effect of mushroom extracellular polysaccharides on fatty acid composition and liver peroxisome proliferator-activated receptor-alpha (PPAR-α) expression in obese-diabetic rats was investigated, and distinguished the association among anti-obesity, hypoglycemic and hypolipidemic properties. Extracellular polysaccharides from three different strains of Pleurotus tuber-regium were extracted and labeled as HP (high-percentage), MP (medium-percentage) and LP (low-percentage). Obese- diabetes (OD) was induced by chronic high-fat diet plus streptozotocin (STZ) injections. Simultaneously to the diet, polysaccharides were orally administered to OD groups (20 mg/kg body weight/8-week), and categorized into OD+HP, OD+MP and OD+LP groups (n = 10/group), respectively. High-fat diet plus STZ-induced hyperglycemia was prominently attenuated by polysaccharides. Increased fatty acid component n-6/n-3 ratio in liver and plasma of obese-diabetic rats was attenuated, while, reduced MUFA/ PUFA and MUFA/SFA ratios were restored (P < 0.01) with polysaccharides treatment. Furthermore, elevated serum total cholesterol, triglycerides and low-density lipoprotein (LDL) concentrations were controlled, and parallel restoration of decreased high-density lipoprotein (HDL) levels were found with polysaccharides supplementation. This hypolipidemic property might be associated with up-regulated liver PPAR-α mRNA expression and protein levels (P < 0.01). These findings concluded that stable fatty acid components and activated PPAR-α by polysaccharides may contribute to its hypoglycemic and hypolipidemic properties. Therefore, P. tuber-regium could be considered as nutritional supplement to treat diabetic complications.