Keratin-associated proteins 8.1 gene (KAP8.1) is a structural gene responsible for the cashmere. KAP8.1 protein contains high glycine and tyrosine, which concerns regulation and function of the matrix structure fiber. In this study, the polymorphism of KAP8.1 gene was detected by methods of aPCR-SSCP (asymmetric polymerase chain reaction single-strand conformation polymorphism) and DNA sequencing in 791 individuals from two breeds. The results showed that there were two mutations in this gene. The mutations were described as c.63 T>G and c.66 C>G, which would result in two synonymous mutations in KAP8.1 protein. The findings go against previous research, in which there was not polymorphism at KAP8.1 gene. The reasons might be that different cashmere breeds were detected in two studies. Further analysis of results leads us to believe that the polymorphism of KAP8.1 gene might be relevant to fiber diameter.