A 77-year-old man presented with poor appetite and dyspnea. A gastroendoscopy showed an advanced gastric cancer and a CT scan demonstrated diffuse interstitial infiltrative shadows in both lungs. Laboratory data showed high level of anti-SSA and anti-SSB antibodies, suggestive of interstitial pneumonia associated with Sjögren's syndrome. Although the levels of KL-6 and SP-D, markers of interstitial pneumonia, decreased after steroid and immunosuppressive therapy, the CT findings of interstitial pneumonia showed no remarkable change. Surgery was performed 2 months after the administration of prednisolone since the respiratory function had improved, allowing the administration of general anesthesia. A CT scan revealed remarkable improvement of the lung lesions after the surgery. Therefore, it is likely that Sjögren's syndrome and interstitial pneumonia manifested as paraneoplastic syndromes in the presented case.