Abstract: Objective To study the techniques for prenatal diagnosis of abnormal chromosomes. Methods Amniotic fluid or umbilical cord blood samples were taken from pregnant women who visited our department from April 2010 to August 2012. Their prenatal abnormal chromosomes were diagnosed by fluorescence in situ hybridization (FISH) and routine chromosome karyotyping, respectively, and compared. Results The average time of chromosome karyotype analysis was 4-5 weeks. Of the 492 amniotic fluid or umbilical cord blood samples that were analyzed, 2 were failed. The chromosome karyotype analysisshowed that the total abnormal chromosomes accounted for 8.74% (43/492), the abnormal chromosomes accounted for 81.40% of the total abnormal chromosomes (35/43), the chromosomes with abnormal structures accounted for 18.60% (8/43), the trisomes 21 and 18 accounted for 74.29% (26/35) and 17.14% (6/35) respectively, the abnormal sex chromosomes accounted for 8.57% (3/35). The average time of FISH was 72-96 h. The FISH showed that the abnormal chromosomes accounted for 7.09% (35/494), and the trisomes 21 and 18 accounted for 74.29% (26/35)and 17.14% (6/35) respectively, and the abnormal sex chromosomes accounted for 8.57% (3/35), which were consistent with those of chromosome karyotype analysis. No abnormal chromosome structure was detected by FISH. Conclusion FISH can diagnose the prenatal abnormal trisomes 21, 18, 13 and sex chromosome monosome and trisome. FISH in combination with chromosome karotype analysis is strategy for understanding the chromosome.