We herein report a case of protein-losing gastroenteropathy in a 77-year-old female patient. She had been diagnosed with Sjögren's syndrome-associated interstitial pneumonia 12 years earlier. Treatment with a low-dose oral glucocorticoid had stabilized the pulmonary lesions. However, dyspnea on exercise progressively increased and was accompanied by the development of leg edema and thoracoabdominal effusion. Consequently, the patient developed hypoproteinemia and hypocomplementemia. Multimodal examination, including thoracoscopy, did not yield any specific findings. Nevertheless, despite the lack of gastrointestinal symptoms, the α₁-antitrypsin clearance rate was elevated, and intestinal protein loss was evident on scintigraphy. Finally, the patient was diagnosed with protein-losing gastroenteropathy. This is a rare complication of Sjögren's syndrome and is occasionally refractory to treatment with glucocorticoids. In the current case, administration of a high-dose glucocorticoid was required to achieve remission. The present case was characterized by protein leakage that developed during the stable stage of Sjögren's syndrome in the absence of typical gastrointestinal symptoms.