A patient with malignant melanoma of the oral cavity who lived for a long period despite developing liver metastasis is presented. An 81-year-old female was referred to our hospital because of a pigmented tumor of the lower gingiva. Under the clinical diagnosis of malignant melanoma, she underwent bilateral functional neck dissection and marginal mandiblectomy. Histological diagnosis of the operation material was malignant melanoma with regional lymph node metastasis. In spite of loco-regional control, liver metastasis developed at 7 months after the surgery. She then underwent combination chemotherapies with dimethyl triazeno imidazole carboxamide (DTIC), nimustine hydrochloride (ACNU) and vincristin (DAV therapy), or cisplatin, DTIC, ACNU and tamoxifen (DAC-tam), but no marked response was obtained. Considering the advanced age of the patient, immunotherapy with a biological response modifier, OK432, alone was started. After administration of OK432, the metastatic tumor gradually decreased, and she is alive without any clinical symptoms of tumor at 46 months after the detection of liver metastasis, although it is still present on ultrasonic and CT examinations.