Introduction: the placenta is a fetomaternal organ that separates the maternal and fetal circulation. It is a vital organ for fetal development and is a mirror of the maternal and fetal status. The essential elements of the placenta are the chorionic villi from the fetal side and the decidual plate from the maternal side. Fetal blood circulates through capillaries in the villi. The villi are surrounded by maternal blood. The maternal and fetal bloods are separated by a very thin placental membrane. The fully formed placenta is ~ 6 inches in diameter and weighs ~ 500 g. Its metabolic functions are complex and it undergoes changes continuously throughout gestation in weight, structure, shape and function in order to support prenatal life. Materials and Methods: a total of 50 gestational diabetic mellitus (GDM) and 50 normal placentae were utilized for the present study. Placental shape was visualized, classified, and the weight, volume, thickness and circumference of the placenta were measured. Tissue for histological examination was taken from central and peripheral zones of the placenta. Microscopic findings, number of villi, diameter of the villi, number of capillaries in each villi, and the diameter of capillaries were noted. Results: macroscopically, there is increase in weight, volume, and circumference of GDM placentae than in the control group. The present study also showed an increase in number and diameter of villi and in the number of capillaries in each villus in the gestational diabetic mellitus placentae other than control group and it is statistically significant. Conclusion: the present study supports that there is very a strong relationship between placenta morphometry and diabetes mellitus.