Epidural neurolysis with phenol has appeared in literature since 1960. Complications due to accidental subdural block is a rare and unexpected sensory and/or motor disturbance, but it does occur. A 74 years old woman had postherpectic neuralgia for 3 weeks and VAS score of 10. She was treated with intercostal nerve block and intravenous infusion of lidocaine for 7 days and VAS score decreased to 6. To proceed further, we decided to perform epidural neurolysis with 4% phenol 1.5 ml. During thoracic epidural catherization, we encountered unexpected subdural catheterization in subdurographic finding, but we could not precisely rule out subdural catheterization. We had to check CT for exact location of catheter tip. We then performed subdural neurolysis with phenol. This procedure reduced VAS score to between 3 and 4, and we removed the catheter. She had no complication.