Pancreatic islet transplantation is a promising therapeutic treatment for type 1 diabetes mellitus. In the present study, we cocultured islets with or without a polyglycolic acid (PGA) fibrous scaffold for 5 days and transplanted the PGA-islet grafts into the leg muscles of Wistar rats with streptozotocin-induced diabetes; controls were injected with saline. The results showed that the blood glucose concentrations of the group given islets embedded with the PGA scaffold were lower than those without the scaffold or controls. On the other hand, the insulin content of the PGA-islet group was higher at all 5 time points compared with the insulin contents of the other 2 groups. After transplantation, many islets in the PGA-islet grafts showed normal morphology (as seen under the scanning electron microscope) and were surrounded by red blood cells. A fibrous extracellular matrix was visible around the PGA-islet grafts. These results demonstrated that PGA-islet grafts improved blood glucose and insulin concentrations in rats with induced diabetes.