Although preeclampsia (PE) is one of the most important problems affecting pregnant women, etiologic factors in its development are still unclear. We aimed to investigate the expression levels of platelet endothelial cell adhesion molecule-1 (PECAM-1) and intercellular adhesion molecule-1 (ICAM-1) in preeclamptic and control healthy placentas. Placental tissue samples were obtained after delivery from patients diagnosed with PE, and from normal term pregnants and analyzed by immunohistochemistry for the expression levels of the two adhesion molecules PECAM-1 and ICAM-1. A strong expression of PECAM-1 in endothelial cells lining the vessel walls of placental villi in placentas of control group was found, but the intensity of PECAM-1 expression was highly reduced in placentas of PE group (p = 0.017). Conversely, a strong expression of ICAM-1 was observed in placental villi in PE, significantly higher than that of normal placentas (p = 0.005). The findings of a decrease of PECAM-1 expression and an increase of ICAM-1 expression in preeclamptic placenta suggest the existence of functional roles of these adhesion molecules in the pathophysiology of PE, probably by contributing to the reduced trophoblast invasion and the increased vascular damage, respectively. Inhibiting ICAM-1 (i.e., with ICAM-1 monoclonal antibody) and promoting PECAM-1 expression may be good therapeutic approaches to prevent PE symptoms in the future.