Placental mesenchymal dysplasia is a rare condition of pregnancy that presents as macroscopic features of molar change in the placenta and normal karyotype fetus. These cases are often misdiagnosed as partial mole. We report a new case of mesenchymal dysplasia. A 27-year-old Japanese primigravida delivered an 820 g female baby (46XX karyotype) without congenital anomalies at 27 weeks gestation due to massive bleeding with placenta previa. The placenta had mimicking partial moles, grape-like vesicles and normal villi that diffusely occupied the area on the maternal surface of the placenta. Pathologically, enlarged stem villi contained loose, moderately cellular connective tissue with focal cistern-like formation, and peripherally located vessels. Abnormal trophoblastic proliferation and trophoblastic inclusions were not observed in any of the sections examined. Some villi contained chorioangiomatoid changes. The mother and child were followed up for more than 5 years and showed no sign of trophoblastic disease or Beckwith-Wiedemann syndrome features.