We reported a case of subchorionic placental cyst with maternal floor infarction in 32-year-old multigravida. In this case the infant without growth retardation was delivered at fuU term by repeat cesarean section. A 5.8*5cm placental cyst detected prenatally by ultrasound was shown subsequentty to be a subchorionic cyst without thrombohematoma. The cyst was unilocular and attached near the cord insertion, and it contained straw-colored fluid. There was no other placental abnormalities except placental inFarction on matemal floor with fibrin deposition. It is necessary to differentiate placental cystic lesions by ultrasonographic and pathologic examination because placental abnormalities could be associated with perinatal complications.