A 69-year-old man experienced general malaise, weight loss, amnesia, gait disturbance, and restlessness a month prior to admission. Brain MRI showed high intensity areas in the bilateral medial temporal lobes and insular cortices on FLAIR images, and therefore, he was diagnosed with limbic encephalitis. After admission, quadriplegia and respiratory failure progressed rapidly, and he needed ventilatory management. A nerve conduction study revealed low compound muscle action potential amplitude with loss of sensory nerve action potential, which indicated axonal sensorimotor neuropathy. We administered intravenous immunoglobulin and methylprednisolone pulse therapy, but he did not recover. Although no tumor was found on CT, his serum was positive for anti-Hu antibody; therefore, we diagnosed him with paraneoplastic neurological syndrome. An FDG-PET study showed accumulation at lesions on two hilar lymph nodes. Small cell lung carcinoma was detected by endobronchial ultrasound-guided transbronchial needle aspiration. Although paraneoplastic acute sensorimotor neuropathy with respiratory failure resembling Guillain-Barré syndrome is rare, identification of antibodies and servey of tumors aids accurate diagnosis.