Cord entanglement is a leading cause of mortality of monochorionic monoamniotic twins. Few studies focused on entanglement features/structure itself. Three-dimensional color Doppler ultrasound was conducted to evaluate the cord entanglement in monoamniotic twins at 30 weeks of gestation. Ultrasound revealed detailed features: the two cords were entangled at several points with a chain-like appearance and this complicated structure led us to closely monitor fetal well-being. Seven days later, non-reassuring fetal heart rate pattern was observed, and cesarean section was performed at 30 6/7 pregnancy week, yielding female infants without neurological sequelae. Three-dimensional color Doppler clearly delineated the features of entanglement, and thus was useful for evaluating cord entanglement in monoamniotic twins.