An immunocompetent 47-year-old man presented with a five-month history of progressive lower limb weakness, back pain, sphincter dysfunction, and intermittent fever, suggesting myelopathy in a chronic deteriorating course. A comprehensive analysis comprising of blood tests, neuroimaging, CSF profiling, molecular analysis, and histopathology was performed. Notably, enhanced spinal cord MRI revealed longitudinally extensive intradural-extramedullary lesions involving the cervical, thoracic, and lumbosacral spinal cord, with homogeneous enhancement and spinal cord compression. Serum treponema pallidumhemagglutination (TPHA) and rapid plasma reagin (RPR) tests were positive. CSF profiling showed pleocytosis, significant protein elevations, hypoglycorrhachia, and positive TPHA test. 18F-FDG-PET/CT indicated slightly increased intraspinal fluorodeoxyglucose (FDG) uptake. Spinal cord biopsy further showed small round blue cells in poorly differentiated tissues. Immunostaining was positive for NKX2.2, CD56, CD99, Synaptophysin, and Ki67 (50%). Molecular analysis detected a novel MALAT-CYSLTR1 fusion protein and variants in oncogenic genes including PTCH1, TERT, CREBBP, SPEN, and STK11. The diagnosis of intraspinal extraosseous Ewing sarcoma (ES) was confirmed. Briefly, our case details the diagnosis of a patient with intradural-extramedullary ES and highlights the value of spinal cord biopsy in progressive myelopathy of unknown causes.