A 6-month-old intact female Bichon Frise dog weighing 0.9 kg presented with vomiting, anorexia, and lethargy persisting for 3 days. No remarkable abnormalities were detected on the history or physical examination. Laboratory findings were mostly normal, except for elevated levels of alkaline phosphatase (ALP) and blood urea nitrogen (BUN). Abdominal radiography revealed a fluid-dilated stomach and gas-dilated intestinal loops in the regional areas. Abdominal ultrasonography was performed to investigate the cause of gastrointestinal dilation, which revealed a rectangular, homogeneous, echogenic foreign material with no shadowing in the small intestine, causing mechanical obstruction. Upon further inquiry involving detailed re-take of history with the owner, a history of ingesting dog gum 4 days prior was identified. On surgical enterotomy, the hard pet food was identified and removed from the distal duodenum. Postoperatively, the patient's clinical signs showed complete improvement, with a return to normal appetite. The present case demonstrates that less-digestible, hard pet food, despite showing no shadowing on ultrasonography, can act as a foreign material, causing mechanical intestinal obstruction in a small-breed puppy. Furthermore, surgical removal of these materials is necessary in cases of intestinal obstruction.