Vitamin A and its derivatives are essential for embryonic development, but an overdose of vitamin A is toxic to the offspring. The placenta is an interface that nourishes and protects the embryo. Although there are numerous publications on the effect of vitamin A on the placenta, there is insufficient information on the changes in the morphology of this organ caused by different doses. The aim of our study was to demonstrate the effect of retinyl palmitate administered at different doses on the volume of the placenta and its component, the decidua. Pregnant rats were divided into 6 groups between gestation day 10 and 12. The first group received 10.000 IU/kg, the second group 20.000 IU/kg, the third group 50.000 IU/kg, the fourth group 100.000 IU/kg and the fifth group 200.000 IU/ kg oral vitamin A. The control group received 1 ml of corn oil on the same days. On day 19 of gestation, placentas were collected and 5 µm sections were stained with Massons’s trichrome. The volumes of total placenta and decidua were estimated using the Cavalieri volume estimation method. All placental volumes of the experimental groups were larger than those of the control groups. The decidual volume increased abruptly at a dose of 50.000 IU/kg and remained higher than the control volume at higher doses. The ratio between the decidual and placental volumes increased at 50.000 IU/kg and was smaller than the control at 200.000 IU/kg. A large placental volume is thought to be an indicator of placental insufficiency. Although our results suggest that an increase in placental volume above 10.000 IU/kg may have a negative effect on placental function, we conclude that the imbalance between decidual and placental volume above 50.000 IU/kg strengthens the suggestion that placental insufficiency may have increased after this dose.