Ganoderma lucidum polysaccharides (GLP), a kind of medicinal mushrooms, were widely used in southeastern countries with putative anti-diabetic effects. In order to unravel the underlying mechanism of its anti-diabetic effect, this study examines the effects of GLP on gut microbiota composition and functions in type 2 diabetes mellitus (T2DM) status. In this study, the effects of GLP on the gut microbiota and fecal metabolites in high-fat diet and streptozotocin-induced T2DM rats were examined by 16S rDNA sequencing and 1H NMR profiling. As a result, administration of GLP led to significant decreases in the levels of fasting blood glucose and insulin. Moreover, GLP treatment reduced the abundance of harmful bacteria, such as Aerococcus, Ruminococcus, Corynebactrium and Proteus, and increased the level of Blautia, Dehalobacterium, Parabacteroides and Bacteroides. The PICRUSt analysis indicated that GLP could restore the disturbed amino acids metabolism, carbohydrates metabolism, inflammatory substances metabolism and nucleic acid metabolism of gut bacterial community in T2DM rats and most metabolic changes observed by metabolomics analysis were consistent with these consequences. Taken collectively, GLP can restore the disordered gut microbiota of T2DM rats to a normal level and modify metabolites of the host to realize its antidiabetic effects. Copyright © 2019. Published by Elsevier B.V.