An 1-year-old, intact female Yorkshire Terrier weighing 1.83 kg was referred for vomiting and anorexia. Survey abdominal radiographs revealed marked gastric distention. Ultrasonography showed a hyperechoic material with acoustic shadowing near the pylorus. A foreign body and ulceration were identified during gastroscopic examination. After endoscopic retrieval of gastric foreign body, unexpectedly abdominal distention was developed. Abdominal radiographs revealed pneumoperitoneum, but no leakage of contrast media was observed in gastrointestinal contrast study. Three days after hospitalization with supportive care, no abnormal findings were detected, and then the dog was discharged. This case describes the development of peumoperitoneum during endoscopic retrieval of gastric foreign body.