To detect if polymorphism could be observed in the hybridization patterns of different sweet potato cultivars,twenty sweet potato cultivars were analysed with two-colour fluorescence in situ hybridization(FISH)using the 45S rDNA and 5S rDNA.The number、region and intensity of rDNA loci on the metaphase chromosmes and interphase nucleus of all materials were observed.The average number of chromosmes in these cultivars is 90,but not always be.19 to 22 45S rDNA signals should be examined,varies among cultivars.