One-year-old and 50 kg male Anatolian Shepherd dog referred to Clinics of Veterinary Faculty of Erciyes University was examinated in this case report. Clinical examinations revealed that the dog had extreme weakening, difficulty in eating and hypersalivation, an apperant mass formation which started at the second molar tooth region and continued till the soft palate and eusophagus. In the radiographic examination, no metastasis in lungs area was observed. No medical and surgical intervention was considered due to tumor expansion, relapsion and the anatomical constructure of the area. During the necropsy, an elastic, lobular structured mass in 15x25.2 cm size and 230 gr weight was seen expanding up to larynx. The examination of the histologic sections from the mass revealed that structures of collagen bunch and wide areas of fibroblast cells were available. Mitotic activity at the sections was evident. In the light of these findings, the case was diagnosed as fibrosarcoma originated from mouth mucosa. As a result, although fibrosarcoma is observed in dogs over than 8 years old, it can also be detected in young dogs, which is less than one years old.