Primary malignant melanoma of the esophagus (PMME) is rare but aggressive. PMME accounts for approximately 0. 1% of all malignant esophageal neoplasms occurring worldwide, and is usually diagnosed during the advanced stage. A 67-year-old man underwent an esophagogastroduodenoscopy (EGD) at our hospital and confirmed 20 mm of black pigmentation in the lower esophagus in the chest area. Pathological biopsy findings of the black-pigmented epithelial tissue revealed the presence of tumor cells with brown granules, leading to the diagnosis of malignant melanoma. Owing to difficulty in accurately diagnosing the range in this PMME case, we performed thoracoscopic esophagectomy. Pathological organisation test results were pT1a-LPM, INFb, pN0, and pM0, which were diagnosed at pStage I. The lesion expanded extensively, measuring > 10 cm in diameter. The tumor cells, which were centrally located in the black-pigmented area, were observed to have proliferated beyond the surrounding brownish area into the mucosa, but no findings were found in the endoscopic examination. As in this case, because PMME may diffusely spread along the basal layer outside the range of pigmentation, endoscopic diagnosis of the extent of disease spread may be impossible; hence, it is important to keep this phenomenon in mind while performing resection to treat PMME.