Diabetes mellitus is one of the prevalent metabolic diseases causing blood microvascular and macrovascular dysfunction. These dysfunctions cause the balance disorder of water and electrolytes in origin organs such as kidney and retina and leading to some complications as retinopathy and nephropathy. This study investigated choroid plexus (CP) volume changes inembryo of diabetic and normal mothers from the appearance time of CP untill birth time in rat. We divided 55 adult female Wistar rats wighing 200-250g into two groups, control and experiential. On the 7th day of pregnancy, hyperglycemia was induced by a single injection (i.p.) of stz (55mg/kg). Control animals were given an equal volume of citrate buffer. After parturition, 1 pup was randomly selected from each litter in days (16.5-21.5), their brain dissected, fixed in 10% formalin, sectioned in 7micro meter thickness, and stained by H&E. By applying stereological techniques and systematic random sampling scheme, the volume of CP was estimated. In comparison with controls, statistical analysis showed significant increase (p<0/05) in the volumes of the CP in embryo from diabetic mothers. Probably the increase of CP volume in diabetic mothers' fetuses is caused by a kind of angiogenesis in blood vessels of this plexus, which is the effect of maternal diabetes.