Fluorescence in situ hybridization(FISH) system was established in Lagerstroemia species,and 45S rDNA loci were anchored on the chromosomes of L.indica,L.caudata,L.fauriei and L.limii.The results showed that only one pair of 45S rDNA loci were found at the end of the short arms of one pair of homologous chromosomes.The karyotypes of the four Lagerstroemia species were all 2A and the karyotype formulas were 2n=48=2M+24m+22sm(L.indica),2n=48=30m+18sm(L.caudata),2n=48=2M+20m +26sm(L.fauriei) and 2n=48=2M+32m+14sm(L.limii) respectively.It is the first report on karyotype analysis with 45S rDNA loci in Lagerstroemia genus and the results will provide a cytomolecular basis for genetic research of Lagerstroemia.