<p><strong><em>Background and Objectives:</em></strong> Previous studies have shown that morphine consumption during pregnancy may delay embryo development or cause the nervous system to function abnormally. The present study focused on the effects of maternal morphine consumption on fourth ventricle and choroid plexus development in Wistar rats.</p><p> </p><p><strong><em>Methods:</em></strong> Wistar rats weighing between 170 and 200 grams were selected for this study. The experimental group after pregnancy received 0.05mg/ml of morphine in their drinking water daily. The control group received only tap water. On day fourteen of pregnancy, the pregnant animals were anesthetized by chloroform and the embryos were removed surgically. The embryos were fixed in 10% formalin for 4 weeks. Then, tissue processing, sectioning and staining hematoxylin and eosin (H&amp;E) were applied on the embryos. The sections were examined for fourth ventricle and choroid plexus development by light microscope and MOTIC software.</p><p> </p><p><strong><em>Results:</em></strong> The results of the study indicated the choroid plexus area in the experimental group increased. Moreover, the fourth ventricle area reduction in the experimental group was significant in comparison with that in control group.</p><p><em> </em></p><p><strong><em>Conclusion:</em></strong> This study showed that oral morphine consumption has can decrease the fourth ventricle and increase choroid plexus area. This defect may delay the functioning and development of central neuron system. such as, changes observed in the fetus born by opioid addicted women.</p><p> </p>