Spinal epidural lipomatosis (SEL) frequently occurs as a result of long-term steroid administration for various disorders, and patients often present with osteoporosis. Acute paraplegia in patients with extensive thoracic SEL is rare. We report a case of acute paraplegia caused by osteoporotic compression fracture with extensive thoracic SEL in a 44-year-old man with rheumatoid arthritis who had received steroid therapy for 4 years. He presented initially with abdominal distension and weakness of lower limbs, and a sudden onset of paraplegia with complete motor and sensory loss below the T6 level ensued. Plain radiographs showed an osteoporotic compression fracture of the T6 vertebra. Magnetic resonance imaging showed osteoporotic compression fractures of the T5 and T6 vertebrae and SEL from T2 to T10 vertebrae. Decompressive laminectomy with epidural fat debulking was performed, and the pathology was confirmed as epidural lipomatosis. His neurological condition showed no improvement below the T6 level 3 months after surgery. Osteoporotic compression fracture is a risk factor for acute paraplegia in patients with thoracic SEL and decompressive surgery should be performed without delay.