Statement of Problems: Helicobacter pylori (H.pylori) is considered to be a pathogen responsible for gastritis and peptic ulcers as well as a risk factor of gastric cancer. Recently, H.pylori has been detected in dental plaques, hence oral cavity has drawn attention to be the second site for H.pylori. However, it is not yet clear whether the oral cavity acts as a reservoir for this bacterium.Purpose: The aim of this study was to clarify whether the oral cavity is the reservoir for H.pylori, and to find out any relationship between gastritis and dental plaque the infection.Materials and Method: In this study, PCR was used for detection of Helicobacter pylori as a non-invasive method with higher sensitivity and specificity. Samples of the supragingival and subgingival dental plaque were collected from 67 patients (44 with periodontitis, and 23 suffered from both gastritis and periodontitis). Using sequences of different H. pylori genes, four pairs of oligonucleotide primers were designed to optimize a sensitive and specific protocol for diagnosis and detection of H.pylori. The data were analyzed using Chi Square and Fisher statistical tests. The level of significancy was considered at p0.05.Results: According to the results of this study, prevalence of H.pylori in dental plaque of the whole samples was low (5.9%), but there showed to be a significant relationship between H. pylori infection in dental plaque of pateints with gastritis ( p<0.05).Conclusion: Although the prevalence of the Helicobacter pylori in dental plaques was shown to be very low, it might be necessary to pay close attention to dental plaques as the possible source of re-infection after treatment of gastritis. It is recommended that in treating gastritis, along with antibiotic therapy, attempts should be made in dental plaque removal and educating patients with proper health practices.Key words: Helicobacter pylori, Dental plaque, Polymerase chain reaction (PCR), Gastritis, Periodontitis.