We present the findings of an early-stage primary mucinous sweat gland adenocarcinoma in the lower eyelid of a Japanese patient. The patient was a 73-year-old man who had had a nodule on the left lower eyelid for two years. He was referred to our hospital with a diagnosis of a swollen chalazion. The clinical and histopathological records were reviewed and the mass was excised. Histopathological examination revealed a mucinous sweat gland adenocarcinoma. Postoperative magnetic resonance imaging and positron emission tomography excluded systemic metastases. After the histopathological findings, a complete surgical excision of the margins of the adenocarcinoma was performed, with histopathological confirmation of negative margins. After the final histopathological examination, the patient was diagnosed with a primary mucinous sweat gland adenocarcinoma of the left eyelid. Six months after the surgery, no recurrence has been observed. Because the appearance of mucinous sweat gland adenocarcinoma of the eyelid is quite variable, the final diagnosis can only be made by histopathological examination. A complete surgical excision is recommended.