Background: The normal fetal growth and survival depend on the proper development and function of the placenta, which serves to maintain a materno-fetal interference for the exchange of blood gases, nutrients and wastes. Preeclampsia is a condition characterized by hypertension and proteinuria after 20th week of gestation. Aim of the work: This study was designed to investigate light and electron microscopic histological changes in preeclamptic placentas.Subjects and methods: Paraffin sections from placenta biopsies were obtained form thirty single fetus pregnancies complicated by pre-eclampsia, stained with hematoxylin and eosin Masson’s trichrome then examined by light microscopy. Quantitative morphometeric studies followed by statistical analysis of the data were done. Biopsies were prepared and examined by transmission and scanning electron microscopy. Results: Light microscopic examination showed that syncytial nuclei were aggregated into knots, sprouts and formed syncytial strands. Villous connective tissue core was condensed with decreased fetal capillaries. Masson’s trichrome stained sections revealed that the villous core was filled with thick collagen bundles. Semi-thin sections stained with toluidine blue of trophoblasts showed cytoplasmic vacuolation, apoptotic nuclei and thick corrugated trophoblastic basement membrane. Statistical studies revealed significant increase in the count of syncytial knots and of collagen content in the villous core. By TEM, syncytial cells showed loss of microvilli and interrupted apical cell membrane. The villous core was studded with collagen fibrils and bundles that encroached in the wall of fetal blood vessels that were lined by swollen ragged endothelial cells and showed atheromatous changes. By SEM, the terminal capillary loops were few, long and straight with no coiling. Webs of fibrin covered the wrinkled syncytial surface. Conclusion: In preeclamptic placentas, ischemic changes with maldeveloped terminal villi occur. These findings might account for impaired gas and nutrient transfer in preeclampsia.