The objective of this study was to investigate polymorphisms of keratin-associated protein 8.1 (KAP8.1) gene and its effect on fibre traits of Chinese Inner Mongolian Cashmere goats. The fibre traits data investigated were cashmere fibre diameter, combed cashmere weight, cashmere fibre length and guard hair length. Five hundred and forty animals were used to detect polymorphisms in the complete coding sequence of the hircine KAP8.1 gene by means of PCR-SSCP. The results identified six genotypes, AA, BB, CC, AB, AC and BC, coded for by three different alleles A, B and C. Two SNPs in the coding region were confirmed by sequencing, which were T113G and G116C respectively. The relationships between the genotypes and cashmere fibre diameter, combed cashmere weight, cashmere fibre length and guard hair length were analyzed. There were significant differences between the associations of the different genotypes with cashmere weight (p<0.01), cashmere length (p<0.05) and hair length (p<0.01). Cashmere fibre diameter was the only trait that was not associated with the genotypes. The animals of genotype AB and BB had the higher cashmere weight compared with the genotype AA. By further analysis, it appeared that the KAP8.1 genotype effects on fibre traits may be due to a mutation at the 113 locus. These results suggested that polymorphisms in the hircine KAP8.1 gene might be a potential molecular marker for cashmere weight in Cashmere goats.