We report a rare case of cauda equina syndrome due to bilateral lumbar facet cyst. A 62-year-old woman has developed both legs sciatica 3 months prior to her visit, but recently motor weakness and voiding difficulty occurred. Lumbar magnetic resonance image showed bilateral lumbar facet cyst compressing and surrounding both L5 nerve root and accompanying spinal stenosis. Urgent decompressive laminectomy and cyst removal was performed. Although sciatica was relieved and motor weakness was recovered usefully. Voiding difficulty and dysesthesia were not improved.