Abstract: Merkel cell carcinoma (MCC) is a rare and highly aggressive neuroendocrine malignant tumor originating from the skin. The author reported a patient with advanced MCC whose local lesions were treated with ¹²⁵I seed implantation, evaluated the therapeutic efficacy by comparing ¹⁸F-FDG PET/CT images before and after treatment. The features of MCC were analyzed from clinical symptoms, imaging findings, treatment process and relevant literature reports, in order to deepen clinicians' understanding of MCC and provide a basis for the local use of ¹²⁵I seed implantation in patients with advanced MCC.