The polymorphism of the CSN1S1 was investigated in three Bulgarian sheep breeds. The study was carried out on total of 90 individuals belonging to Karakachanska, Local Karnobatska and Copper-Red (Mednochervena) Shumenska, that are the most popular local sheep breeds in the country. Two genetic variants of CSN1S1 (A and C) and three genotypes (AA, AC and CC) have been identified using PCR-RFLP analysis. The gene frequencies of CSN1S1 A and C were 0,02 and 0,98 in Karakachanska and Copper-Red Shumenska, and 0,10 and 0,90 in Local Karnobatska breeds, respectively. The most common genotype at the αS1-CN locus was CC with frequencies 0,97 in Karakachanska and Copper-Red Shumenska breeds, and 0,84 in Local Karnobatska sheep. These data provide evidence that Bulgarian sheep have a genetic variability, which opens interesting prospects for future selection programs, especially for marker-assisted selection as well as for preservation of the genetic diversity of the populations of these local sheep breeds.