Our extensive basic research on photodynamic therapy (PDT) application in models of intracranial malignant astrocytoma led to its clinical application for intracranial malignant astrocytoma in Japan. Having considered the safety and effectiveness of this pathology, we initiate a first-in-human clinical study of PDT for spinal cord malignant astrocytoma. This study has an open-label, single-arm design. The initial follow-up period is 12 months, at the end of which we will quantify survival after PDT for spinal cord malignant astrocytoma as primary objective. The secondary objective is to quantify the overall progression-free survival of treated patients and the percentage of patients surviving 6 months after PDT without recurrence. Twenty patients suffering from spinal cord malignant astrocytoma will be recruited. In particular, 10 of those should be newly diagnosed World Health Organization grade 4. After obtaining consent, each patient will receive a single intravenous injection of talaporfin sodium (40 mg/m²) 1 day before tumor resection. One day after completing tumor removal, the residual lesion and/or resection cavity will be irradiated using a 664-nm semiconductor laser with a radiation power density of 150 mW/cm² and a radiation energy density of 27 J/cm². The procedure will be performed 22–26 hours after talaporfin sodium administration. This study protocol has been reviewed and approved by the Certified Committee in the Japanese Ministry of Health, Labor, and Welfare University Hospital Medical Information Network Clinical Trials Registry (Japan Registry of Clinical Trials number, jRCT2021220040).