The present study aimed to investigate the presence of polymorphism at four known genes controlling ovine prolificacy i.e. BMP15, GDF9, BMPR1B and B4GALNT2 in a sample of 115 Iranian Mehraban ewes and their association with litter size (LS) and lambs' birth weight (BW) traits. Using Sanger sequencing of exons and polymorphism specific genotyping, ten SNPs (Single Nucleotide Polymorphisms) were observed in only two genes, GDF9 and BMPR1B. Seven SNPs were found in the GDF9 gene on the chromosome 5. Among them, six were already described in the coding sequence, and a new one (g.41840985C>T) was found in the 3'UTR. In the BMPR1B gene on the chromosome 6, three novel SNPs were detected in the exon 7 (g.29382184G>A; g.29382337G>A and g.29382340G>A). Allelic frequencies were established for six SNPs among the ten identified and they were in Hardy-Weinberg equilibrium. A significant association was found between the novel SNPs found in the exon 7 of BMPR1B and LS. Present results indicate the potential role of the BMPR1B locus in controlling prolificacy of Mehraban sheep and provide genetic markers for further exploitation in selection to improve reproductive efficiency.