Hypoglycemic effect of Juglans regia leaves has been was reported in other previous researches. This study investigated the effect of Juglans regia leaves ethanolic extract on Cerebrum in 18 and 20 day old fetus of diabetic mother. A total of 32 Sprague-Dawley female rats became diabetic by intraperitoneal injection of streptozotocin (50 mg/kg). The animals were divided randomly into four groups. Rats in all groups became pregnant by natural mating. After formation of the nervous system, eight fetuses were obtained after anesthezing animals on the 18th and 20th gestational days in each group; the animals were euthanized, their birth weights recorded and cerebrum samples were taken and fixed. Tissue sections were prepared by routine procedures and different histological parameters were examined. Results revealed a significant decrease in number of cells in gray matter and white matter, ratio of gray matter to white matter and thickness of gray matter at 18 and 20 days in cerebrum of diabetic rats fetus as compared with other groups. The body weight of diabetic control was significantly (P<0.05) more than that of the other group. The present study demonstrates that alcoholic extract of walnut leaves possesses significant antihyperglicemic properties, thus suggesting its beneficial effect in the treatment of maternal diabetes.