The chromosomes of Pacific abalone,Haliotis discus hannai,were examined by C-banding and fluorescence in situ hybridization(FISH)with human major rDNA(18S-5.8S-28S)as probes.The chromosome set of Pacific abalone was composed of 7 pairs of metacentric chromosomes,8 pairs of submetacentric chromosomes,and 3 pairs of metacentric/submetacentric chromosomes.Stable centromeric C-bands were present on 8 pairs of chromosome.Inter metaphase polymorphic telomeric C-bands and heteromorphic pericentric C-bands were found on 5-7 pairs and 3 pairs of chromosomes,respectively.In addition,4 major rDNA loci were mapped onto the telomere of four pairs of chromosomes(2S,7S,12S and 18L).These results provided new markers and characteristics to distinguish chromosomes in the genome of Pacific abalone,and would serve as basic data for further researches on chromosome evolution in abalone.