Helicobacter are spiral-shaped or curved Gram negative bacteria that inhabit the glands, parietal cells and mucus of the stomach. The large gastric HLO ie, H. felis, H. bizzozeronii, H. salomonis, H. heilmannii have been found in the gastric mucosa of dogs. The reported prevalence of HLO infection in pet dogs is about 67 to 86%. However, this study is first report of natural infection of gastric HLO. In this research, we examined 40 healthy stray dogs randomly. Twenty of them were females and 7 of them were immature. All dogs were healthy and they have good appetite. CBC was normal. Endoscopic examination was established for taking of brush cytology after 16 hours fasting. All gastric specimens were taken from body and antrum area. They were examined by Gimsa's and gram's staining at the same time by light microscope. Specimens also used for urease test too. HLO were seen in many of these specimens. The percentage of infection was high and even was seen in the immature stray dogs. By light microscopic taxonomy evaluation, different shapes and co-infection of gastric HLO were detected. The occurrence of gastric HLO infection was similar to the prevalence of these organisms in the pet dogs that suggested for pets in references books. The aim of this study was detecting of the prevalence of natural infection of gastric HLO in stay dogs with brush cytology. With attention to the result; presence of HLO is similar to pet animals. Brush cytology appears an effective method to detection of HLO. This method is safer than biopsy and available. Determination of HLO with this method is simple and seems have a correct results because of large spiral shape of these organisms. Further more, the prevalence of HLO in our stray dogs is high and there are no differences between prevalence of HLO healthy pet dogs (as reported in the references) and our study.