Abstract: Single nucleotide polymorphism in exon 1 of the estrogen receptor （ESR） gene was detected by PCR-SSCP in high fecundity Hu sheep breed. The results indicated that there were three genotypes （AA，BB，AB） in Hu sheep and the frequency of allele A and B was 0.554 and 0.446，respectively. Comparison with the AA genotype，sequencing revealed a C→G mutation at 363 bp of exon 1 of ESR gene in the BB genotype. The Hu sheep with AB genotype or BB genotype had 0.98 and 1.47 more lambs than those with AA genotype，respectively. These results showed that the estrogen receptor locus was a major gene that controlled the prolificacy in Hu sheep or a mark in close linkage with such a gene.

Key words: Hu sheep（Ovis aries）, prolificacy, candidate gene, estrogen receptor gene, PCR-SSCP