Nasal lymphoma, which is one of the most frequently detected nasal tumors in cats, is generally reported to be of B lymphocyte origin and high grade. In lymphoma cases where histopathology and immunohistochemistry have an important place in the diagnosis, radiochemotherapy is gaining more and more importance compared to traditional protocols. In this study, it was aimed to present the clinical and pathological findings of a case of nasal lymphoma and the results of radiotherapy in a cat with neoplasia spreading from the right maxillary region to the frontal region including the nasal cavity and facial deformation in clinical examination. Medical treatment for blood values was applied for premedication in a 7-year-old female tricolor cat with anorexia, respiratory distress and severe anemia. A biopsy sample was taken under general anesthesia and sent to the pathology laboratory. Immunophenotyping was performed to create a targeted treatment protocol for a tumor with histopathologically round cell morphology and high grade malignancy. Immunohistochemical marking method was applied with Vimentin, Cytokeratin, CD3 and CD79a antibodies. The target volume of the patient who was diagnosed with B-cell nasal lymphoma after immunohistochemistry was determined, and computed tomography imaging was performed for radiotherapy planning and metastasis research. Twelve fractions of 300 cGy were determined with radiotherapy sessions 3 days a week. Despite the favorable clinical course of the patient, the treatment for the recurrence of malignant neoplasia was continued with chemotherapy. Information on the classification and treatment of highly malignant and common nasal lymphoma cases in cats is still limited. Chemotherapy and radiotherapy are known to be effective for lymphoma in cats. However, we think that the combined radiochemotherapy protocol is a promising method because it is well tolerated and has the potential to reduce the possibility of possible recurrence due to the progressive character of the tumor. We believe that achieving a 455-day remission in the combined treatment of the patient with radiotherapy and chemotherapy, whose clinical symptoms have decreased and his quality of life has improved significantly since the beginning of the treatment, may contribute to the science of veterinary oncology.