Background & Objectives: Previous studies indicated that morphine consumption during pregnancy could inhibit embryos development. Present study further evaluated the effects of oral morphine consumption on the maternal and fetal portion placenta cells development in Wistar rats.

 Methods: Female Wistar rats (W: 170-200 g) were used in the present study. Morphine group were received morphine (0.05 mg/ml of tap water) after one night coupling with male rats for mating. On 14^th, 17^th days of pregnancy, the pregnant animals were killed with chloroform and the placentas and uterus were removed surgically and fixed in 10 % formalin. The fixed placentas and uterus were stained by H & E method and evaluated for their development. The thickness of layers, as well as number of the cells in both maternal and fetal parts of the placentas was determined by light microscopy and processed using MOTIC software.

 Results: The results indicated that oral consumption of morphine compared to control group, increased the thickness of the layers in maternal portion and also, increased the number of the cells in both maternal and fetal portion of the placenta.

 Conclusion: All together, oral morphine consumption may inhibit placenta cells development and disturb their natural functions. These abnormalities observed in the placenta by opioid addicted pregnancy Wistar rats.