The study was carried out in a pedigree herd of 8 boars and 207 sows of the Polish Landrace breed. The polymorphism of the ESR gene was found by means of the PCR-RFLP method. The amplification resulted in a product of 120 base pairs. The product was then digested with the PvuII restriction enzyme. The two alleles of the ESR gene were identified – ESRA allele – 120 bp, ESRB – 65 and 55 bp. The frequency of ESRA was 0.9419, whereas that of ESRB was 0.0581. The frequency of the AA genotype was 0.8837, whereas that of AB was 0.1163. The ESR BB genotype was not found in the pig population under study. The study focused on the relation between ESR/PvuII genotypes and the number of teats on the left and on the right side, total number of teats in sows, number of piglets in the 1st, 2nd, 3rd, 4th and 5th litters and farrowing age of the first five litters. The initial data for calculations were transformed from the discrete scale to the normal one. The analysis of the relation between the ESR genotypes and reproduction performance characters in the pedigree pigs in five subsequent litters showed small and statistically insignificant differences between the sows of ESR AA and ESR AB genotypes.