Abstract: In order to study the genetic effect of the ESR gene in the whole production cycle of Large white，the polymorphism of ESR in 472 sows were detected, the association between 1774 litters record on litter size and genetic effect were analysised. The results showed that the frequency of AA, AB and BB genetypes were 0.206, 0.572 and 0.222, the AB genetype with the highest frequency; the B allele of ESR gene with the frequency 0.507 was higher than A allele with the frequency 0.493. Through analysis of different parities, the AB genotype had much higher number of born alive than AA and BB genotypes at the first parity, the BB genotype had much higher number of born alive than AA and AB genotypes at the second parity, the AB and BB genotypes had much higher number of born alive than AA genotype at the third parity, the AA genotype with the highest number of born alive at the forth to the seventh parities except for the fifth parity，the AB genotype with the highest number of born alive at the rest parities the AA later parities and all of the parities，showing a certain regularity, but with no significance in all of the parities.

Key words: Large white; ESR; NBA