Abstract: The relationship between MC4R gene polymorphism and body weight in beagle dogs was analyzed. Using gene-specific primers based on canine MC4R exonic sequences a gene fragment was PCR amplified, cloned and sequenced to identify potential polymorphisms. The relationship between a MC4R gene polymophism detected by PCR-RFLP and canine body weight was analyzed. Three variants were found in beagle dog MC4R DNA sequence, of which two were deletions and one was a transversion which created a PshAⅠ site that could be detected by PCR-RFLP. A statistically significant relationship between this polymorphism and body weight was found. MC4R gene could be a candidate modifier gene for canine body weight.