A 12-year-old, castrated male, mixed dog presented with a history of gradual abdominal distention for a year and anorexia recently, with abdominal radiographs showing a gastric pylorus distention. A solitary, pedunculated, heterogeneous mass arising from the mucosal layer in the pylorus with intact wall layers was identified during ultrasound and computed tomography. The gastric muscular layer was evenly thick. After surgical excision of the mass, histological examination confirmed hypertrophic pyloric gastropathy with polypoid growth and Helicobacter spp. infiltrating the gastric mucosal epithelium. This is the first reported diagnostic imaging case of hypertrophic pyloric gastropathy with Helicobacter spp. in a dog.