Background and Objective: Previous studies have shown that morphine consumption during pregnancy may delay the embryo development and/or cause abnormal nervous system function. The present study focused on the effects of maternal morphine consumption on the brain vesicles Prosencephslon and Rhombencephal development in Wistar rat embryos. Material and Methods: A total of 12 female Wistar rats (170-200g) were used in this study. After pregnancy, each rat in the experimental group (n= 6) received 0.05 mg/ml of morphine by tap water, while the animals in the control group only received water only. On the 10th day of pregnancy, the pregnant animals were anesthetized by chloroform and the embryos were removed surgically. The embryos were then fixed in 10%formalin for one week, followed by tissue processing, sectioning, and staining with hematoxylin and eosin (H&E) for each embryo. The sections were examined for primary brain Rhombencephal and Prosencephslon vesicles, and the brain layer development or thickness was examined by light microscopy and MOTIC software. Results: A severe reduction of the area for Rhombencephal and Prosencephslon was observed in the experimental group compared with the control group. Furthermore, the increase in the brain layer thickness was significantly more apparent in the experimental groups in comparison to the control group (P<0.05). Conclusion: Our results show that oral morphine consumption causes a decrease in the primary brain vesicles. This defect may be the cause of abnormal central neuron system function and development observed in the fetuses born from opioid addicted women.