Abstract: An 11-year-old female Chinese Rural dog weighting 10.5 kg presented to the clinic with complaint of a giant mass on her abdomen. In order to clarify the nature of the mass for the diagnosis and treatment, clinical basic examination, hematological examination, imaging examination, histopathology methods were used for the diagnosis; the treatment was carried out, combined with the diagnosis results for treatment. The results showed that the dog had severe anemia symptoms, and the preliminarily diagnosis was mammary gland tumor based on clinical characteristics. Through palliative therapy and partial mastectomy, the mammary gland tumor was successfully removed and the dog’s physical signs were stabilized. Observation of histopathology tissue section was suspected to be a mixed mammary gland tumor without obvious signs of malignancy. Nine months after the operation, the dog was in stable condition and the quality of life was improved. The results suggested that the giant mammary gland tumors could be treated through tumor resection and palliative therapy.