A 7-year-old neutered male, domestic shorthair cat presented anorexia and lethargy. The complete blood cell count revealed severe non-regenerative anemia, lymphocytic leukocytosis, neutropenia, and thrombocytopenia. On the peripheral blood smear examination, medium to large lymphoblastic cells with moderate amounts of basophilic cytoplasm were observed in up to 70% of peripheral leukocytes. Feline leukemia and immunodeficiency viruses were not detected using a commercial diagnostic kit. While splenomegaly and blunt margins of the caudoventral liver were observed in abdominal radiography, changes in the intra-abdominal lymph nodes were not remarkable. Ultimately, flow cytometric immunophenotyping from the peripheral blood revealed a negative for B-cell markers (CD21-/CD79a-) and T-cell markers (CD3-/CD4-/CD5-/CD8-). Based on the hematological examination and the immunophenotyping assay, the cat was diagnosed with non-B, non-T acute lymphoblastic leukemia. Here, we report a rare case of non-B, non-T acute lymphoblastic leukemia to raise awareness and provide information on clinical symptoms and laboratory test and immunophenotyping analysis results.