Ipomoea batatas cv.Xushu 18 and its two wild relatives I.hederacea Jacq.from American and Hong Kong in China were studied by DAPI banding and rDNAfluorescence in situ hybridization.The DAPI banding showed the karyotype of Ipomoea batatas and I.hederacea Jacq.from American and Hong Kong in China are 2n=6x=90=72m+18sm(18SAT) with satellites on chromosome 1,3 and 6;2n=2x=30=30m(4SAT);2n=2x=30=20m+10sm(4SAT),both with satellite on chromosome 6 and 12,respectively.The FISH data indicated that three pairs of 5S rDNA signals,located on centromere,pericentromere and the telomere of chromosome respectively of Ipomoea batatas;Two pairs of 45S rDNA signals,located on chromosome 6 and 12 were detected on both I.hederacea Jacq.;While 1 pairs of 5S rDNA signals presented on chromosome 6 of I.hederacea Jacq.from Hong Kong,2 pairs of 5S rDNA signals occurred on the chromosome 6 and 12 of that from American.Taking all the data obtained in the study,both I.hederacea Jacq.were distant from the sweet potato,and there were some differentiations in the chromosomes of the I.hederacea Jacq.from different territories.