The study aimed at analysing the OLA-DRB1 (exon2/microsatellite sequence in intron2) gene polymorphism in Polish Heath Sheep and the influence of particular alleles on lamb body weight and weight gain. A total of 45 ewes, 7 rams and 100 lambs of Polish Heath Sheep were examined. In the parental generation 36 alleles of the OLA-DRB1 were found and the most frequent were 466bp, 500bp and 566bp (0.058, 0.125 and 0.067, respectively). In the investigated lambs there were 30 alleles with the highest frequency of 498bp, 500bp, 560bp and 566bp alleles (0.105, 0.210, 0.075 and 0.085, respectively).The presence of certain OLA-DRB1 alleles in ewe and lamb genotypes was found to be associated with significant differences in lamb rearing results. The significant or highly significant influence on body weight at birth and weight gain during the first month of lamb's life were observed in the case of the following alleles: 464bp, 466bp, 470bp, 488bp, 494bp, 538bp and 576bp in lambs; 468bp, 470bp, 474bp, 514bp, 536bp and 548bp in ewes.