Objective To investigate the effect of fluorescence in situ hybridization (FISH) in increasing the accuracy and detection rate of chromosome aneuploid from spontaneous abortion specimens.Methods Chromosome 13,21,16 and 22 single sequence probes and centromere probes of 18,X and Y chromosome probes were used to detect 100 cases of spontaneous abortion villi samples.The results were compared with conventional karyotype analysis.Results (1) Karyotype analysis:Among 89 successfully cultured villi samples,51 abnormal karyotypes (57.3％) were found,including 37 cases of autosomal aneuploidies,four sex chromosome aneuploidies,two triploids,one tetraploid,one 68,XX and six chromosome structural aberrations.(2) FISH:The detection rate of abnormal karyotype was 38.0％ (38/100),among which 25 cases were autosomal aneuploidies,five sex chromosome aneuploidies,three triploids,four XX chimeras and one triploid in chromosome 13,16,18 and 21.(3) Comparison of the two methods:Among the 11 samples which failed by conventional method,FISH found two abnormal samples.In specimens of 46,XY,three cases showed mosaicism by FISH.In specimens of 46,XX,two cases showed chromosomal abnormalities by FISH.FISH detected overall 65.5％ (38/58) of the chromosomal abnormalities.Conclusions FISH combined with conventional chromosome analysis could improve the accuracy and detection rate of abnormal karyotypes in spontaneous abortion specimens.