Objective(s): The Muller cell is the principal glial cell of the vertebrate retina. The expression of Glial fibrillary acidic protein (GFAP) in the Muller cells was used as a cellular marker for retinal damage. This study was done to evaluate the effect of gestational diabetes on retinal Muller cells in rat's offspring. Materials and Methods: In this experimental study, 12 Wistar rat dams were randomly allocated in control and diabetic groups. Gestational diabetes was induced by 40 mg/kg/body weight of streptozotocin at the first day of gestation, intraperitoneally. Dams in control group received an equivalent volume normal saline. Eye of six offspring of each group were removed at postnatal day 28 (P28). The histopathological changes in retina were examined through H&E staining and ultrastructure transmission electron microscopy (TEM). The expression of GFAP was examined using Immunohisto-chemical staining of GFAP in Muller cells. Photographs of retina were taken using Olympus BX51 microscope and a digital camera DP12 and EM LEO906; Zeiss, Germany. Results: In the control rat's offspring, GFAP expression was not significant in Muller cells. According to the optical microscope images, GFAP expression was observed in the processes of the Muller cell in the inner plexiform layer of retina in offspring of diabetic mothers. In TEM technique, nuclear fragmentation and apoptotic bodies were observed in Muller cell of diabetic offspring. Conclusion: This study showed that the uncontrolled gestational diabetes can increase GFAP expression in Muller cells and retinal thickness of retinal layer in rat offspring's, therefore uncontrolled gestational can damage the Muller cells.