We reported a rare case of malignant parotid tumor with a severe granulocytosis, which was induced by granulocyte colony stimulating factor (GCSF) produced from tumor cells. A 59-year-old male patient had shown a marked leukocytosis with up to 27,100/mm3 and a larger number of mature granulocytes in peripheral blood leukocytes. The level of G-CSF in serum was obviously high (263.0 pg/ml). We undertook a total parotidectomy and left radical neck dissection, but the tumor resection was not completely performed because of an extensive invasion to the left carotid artery and parapharyngeal space as well. The pathological diagnosis was poorly-differentiated adenocarcinoma. The patient died about 4 months after being admitted to our hospital, even though a systemic chemotherapy was followed after the surgical treatment. We diagnosed this case as a G-CSF producing malignant parotid tumor, because high G-CSF activity was detected in the tumor secretion, cancerous pleural effusion and culture supernatant of tumor cells, respectively. This diagnosis was further confirmed by the finding that GCSF gene transcripts were detected in tumor cells of this patient.