Down syndrome is the most common autosomal abnormality disease which has multiple congenital anomalies, occurring in 1 of every 800 liveborn infants. Neonates who are affected with this disease comprise majority of the mentally retarded children. To prevent the birth of this congenital anomaly, prenatal diagnosis of Doen syndrome is important. We experienced a case of Down syndrome, diagnosed by fluorescence in situ hybridization(FISH) in pregnancy for 15 weeks 6 days. We report here eith a brief review of the literatures.