A 53-year-old woman with chief complaints of vomiting and constipation was given a diagnosis of ileus and admitted to a local hospital. The origin of the ileus was unknown despite intensive examinations. However, her chest X-ray film and CT showed left hilar and mediastinal lymphadenopathy. Her pro-gastrin-releasing peptide (ProGRP) levels were elevated. After transfer to our hospital, the diagnosis of small cell lung cancer (SCLC) was confirmed by transbronchial aspiration cytology. Since no cause of ileus was found on laparotomy, her symptoms were considered to indicate chronic intestinal pseudo-obstruction (CIPO), a manifestation of paraneoplastic neurological syndrome. Serum anti-Hu antibody testing was positive. Chemoradiotherapy induced complete remission and her abdominal symptoms markedly improved. This is a very rare case of CIPO accompanied with SCLC, which improved after immediate anti-tumor therapy for lung cancer.