A case of malignant melanoma of the nictitating membrane in a 10-year-old cat is described. The primary unilateral tumour mass appeared to originate from the surface of the nictitating membrane, with infiltrative growth in the orbital cavity, resulting in exophthalmia. No ocular involvement was noted. Metastatic spread was seen in the cerebrum and the lungs. To our knowledge, this is the first reported case of a metastasizing melanoma originating from the nictitating membrane in a cat.