Abstract： Objective　To investigate the prenatal diagnosis of trisomy 21 syndrome using chromosome 13/21α satellite probe fluorescence in situ hybridization (FISH) on uncultured interphase cells from amniotic fluid. Methods　The interphase amniocytes of 10 fetuses who were detected normal and 3 fetus who were detected trisomy by prenatal cytogenetic diagnosis were selected. We did FISH which used chromosome 13/21α satellite probe directly on the uncultured amniocytes of these 13 samples. Results　The total rate of the hybridization was 36.7% and 38.6% in control group and observation group respectively, showed no significantly difference. There were four signals in the nucleus, two groups were 36.5% and 3.9% respectively,there were five signals in the nucleus, two groups were 4.0%and 36.1% respectively. The control group and observation group showed significantly difference by the statistical χ2 values (P<0.01).Trisomy 21 syndrome was diagnosed when nucleus of five signals accounted for more than 36.1%. Conclusion　FISH with Chromosome13/21α satellite probe is a valuable method for rapid prenatal diagnosis of trisomy 21syndrome.