Melatonin is a hormone that regulates circadian rhythms and many of the reproductive aspects of mammals and is secreted by the pineal gland during the hours of absence of light. This hormone has high affinity receptors coupled to G-like proteins, termed MT1. A polymorphism of the sequence coding for these receptors was involved in the control of seasonal reproduction in sheep. The purpose of this study was to determine the presence of MT1 receptor polymorphism in Araucana creole sheep, a local breed with a short reproductive anestrus. To carry out this work, we used a technique called polymerase chain reaction-restriction fragment lengh polymorphism PCR-RFLP, for which samples were obtained from genomic DNA of 50 Araucana sheep, which were digested with Mnl1 restriction endonuclease. It was possible to identify the presence of MT1 receptor polymorphism in Araucana sheep. The genotypes were found in a genotype frequency of 68% for genotype + / +, 28% for genotype + / - y4% for genotype - / -. This high percentage of animals with genotype + / + could explain the short reproductive anestrus featuring this breed.