Helicobacter are spiral-shaped or curved Gram negative bacteria that inhabit the glands, parietal cells and mucus of the stomach. The large gastric HLO in dogs are indistinguishable by light microscopy, where they are seen as large, 5 -12µ long spirals. H. felis, H. bizzozeronii, H. salomonis, H. heilmannii have been found in the gastric mucosa of dogs. The prevalence of HLO infection in dogs is 67 to 86% of clinically healthy pet dogs, 74 to 80% of dogs presented for investigation of recurrent vomiting, and 100% of healthy laboratory beagles. 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 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. 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 aim of this study was detecting the rate of gastric HLO infection in dogs with brush cytology. 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. But this method only shows the existence of these organisms and we are not able to confirm the presence of ulcers and erosions that are produced by these organisms.