Oxidative stress is one of the major factors in induction of pancreatic β-cell apoptosis and diabetes. Here, we investigated systematically the roles of a proteoglycan (namely, FYGL) from Ganoderma lucidum in protection and repair of pancreatic β-cells against oxidative stress-induced injury and apoptosis on molecular, cellular and animal basis. FYGL in vitro had antioxidant activity in terms of scavenging of free radicals and reduction power. FYGL improved cells viability, insulin secretion, redox indicator expressions, and mitochondrial membrane potential in H 2 O 2 -induced INS-1 cell via regulating the activations of apoptosis-related mitogen-activated protein kinases (MAPK) and nuclear factor kappa B (NF-κB) pathways as well as the insulin secretion-related pathway. Thrillingly in vivo , FYGL repaired the injured pancreas, reduced the pancreatic β-cells apoptosis, and improved insulin secretion because of regulating the balance of oxidation-reduction, therefore well managed blood glucose in db/db diabetic mice. These results demonstrated that FYGL is promising to be used as a novel natural remedy for protection of pancreatic β-cells against oxidative stress in diabetes treatment. • FYGL has antioxidant activity for its scavenging of free radicals and reductive power. • FYGL protects INS-1 cells against oxidative stress-induced apoptosis. • FYGL regulates the MAPK, NF-κB and insulin secretion-related signaling pathways. • FYGL repairs the injured pancreas and controls blood glucose in db/db diabetes mice. [ABSTRACT FROM AUTHOR]