Veterinary radiotherapy is a modality of cancer therapy which is not well known in Brazil. However, it has been shown high rates of success in Europe and North America, where the search for pet radiotherapy has increased as more and more pets have cancer. The goal of radiotherapy treatment is to administer a sufficiently high radiation dose to the tumor to reduce the surviving fraction of clonogenic tumor cells to zero (biologic basis of radiotherapy). Normal and malignant lymphocytes are extremely radiosensitive. While most cell types must undergo cell division before expressing lethal radiation damage, lymphocytes are among the few cell types that undergo an interphase death when exposed to clinically relevant doses of radiation therapy. Radiation therapy sources are: X-ray, gamma ray or electron ray. It can be delivered by orthovoltage x-ray machines, cobalt-60 machines and linear accelerators. A five years old female cat was referred to Instituto Dog Bakery de Medicina Animal on September 2008 with type B nasal lymphoma (diagnosis was made with immunohistochemistry). The cat was previously submitted to chemotherapy with Elspar®, showing short time of cancer control (treatment was made by another veterinarian and we do not know the exact time duration of control). At the moment of our assessment, Tammy was being treated with Leukeran® (three times a week) and Decadron®. Despite of that, the tumor was growing fast above nasal plane and right eye, which had complete occlusion and lots of purulent secretion. The cat was treated with orthovoltage radiation therapy. It received a dose of 300 cGy three times weekly totalizing five applications. It was used 140 KVp, 18 mA, with 30cm of distance between the machine and the treated area. Tumor size reduced slowly, occurring total remission after five sessions of radiotherapy. It was stabled for 2 months. Afterwards, there was recurrence of the tumor and cat has been treated again with radiation therapy. In literature it is shown the use of radiation therapy in the treatment of nasal lymphoma with total dose of 6-40 Gy. In our study, cat was treated with lower total dose, which could contribute for the short time of remission observed. In conclusion, radiotherapy is a possible treatment choice for feline nasal lymphoma.