Diabetes mellitus (DM) is a chronic metabolic disease characterized by hyperglycemia with defects in insulin secretion and/or insulin resistance. Despite great efforts that have been made in the understanding and management of diabetes, its prevalence continues to grow. Recent discoveries have opened up an exciting opportunity for developing new types of therapeutics from medicinal mushrooms to control DM and its complications. To date, more and more active components including polysaccharides and their protein complexes, dietary fibers, and other compounds extracted from fruiting bodies, cultured mycelium, or cultured broth of medicinal mushrooms have been reported as to having anti-hyperglycemic activity. These compounds exhibit their antidiabetic activity via different mechanisms. This article presents an overview of the multiple aspects of diabetes mellitus and the efficacy and mechanism of medicinal mushrooms for glucose control in diabetes, including the inhibition of glucose absorption, protection of beta-cell damage, increase of insulin release, enhancement of antioxidant defense, attenuation of inflammation, modulation of carbohydrate metabolism pathway, and regulation of insulin-dependent and insulin-independent signaling pathways. However, there is insufficient evidence to draw definitive conclusions about the efficacy of individual medicinal mushrooms for diabetes. In addition, the wide variability, the lack of standards for production, and the lack of testing protocols to assess product quality are still problems in producing medicinal mushroom products. Moreover, well-designed randomized controlled trials with long-term consumption are needed to guarantee the bioactivity and safety of medicinal mushroom products for diabetic patients.