Abstract: The chromosome numbers and karyotypes were observed, and compared in offsprings of backcross of purse red carp （hybrids of common carp Cyprinus carpio and crucian carp ♂ Carassius auratus × purse red carp 8 Cyprinus carpio var. wuyuanensis） by intraperitoneal injection of phytohemagglutinin （PHA） and colchicines to evaluate the chromosome genetics of the offsprings. The results showed that the chromosome numbers of the two backcross offsprings of common carp and crucian carp were both 150, and divided into four chromosome groups of each being consisted of 3 homologous chromosomes, depending upon the position of centromere. In the backcross offsprings of the purse red carp, chromosome numbers and karyotypic formula were expressed to be 3n = 150, NF=252 and 3n=66m＋36sm＋18st＋30t. The backcross offsprings of common carp, chromosome numbers and karyotypic formula were found to be 3n=150, NF=234 and 3n =60m＋ 24sm＋ 36st＋30t.

Key words: backcross, Purse Red Carp, Common Carp, chromosome karyotype