We report two cases of a complete hydatidiform mole coexistent with a live fetus diagnosed by DNA polymorphism analysis. A 27-year-old woman revealed symptoms of pre-eclampsia and ultrasound showed multicystic tumor and placenta coexistent with a live fetus at 16 weeks' gestation. The placenta with partly hydropic change and the fetus without anomaly were consequently evacuated. Another 30-year-old woman had a multicystic mass attached to a normal placenta with a 20-week live fetus on ultrasound examination. A hysterotomy was carried out because of persistent bleeding due to placenta previa. In both cases, DNA was extracted from the placental tissue and the tumor, as well as from maternal and paternal blood. Genetic analysis demonstrated that the placental tumor consisted of only paternal origin, which is consistent with the diagnosis of complete hydatidiform mole.