Gastrointestinal lesions have been extensively reported in wild and captive marine mammals. However, their etiology remains unclear. In humans and other animals, chronic gastritis and peptic ulcers have been associated with Helicobacter sp. Therefore, the aim of our study was to investigate the presence of Helicobacter sp. in the gastric juice, dental plaque, and saliva of marine mammals living in a controlled environment. Five dolphins (Tursiops gephyreus), one killer whale (Orcinus orca), one false killer whale (Pseudorca crassidens), three sea lions (Otaria flavescens), two elephant seals (Mirounga leonina), and two fur seals (Arctocephalus australis) were studied. Saliva, dental plaque, and gastric juice samples were examined for Helicobacter sp. using polymerase chain reaction. None of the gastric juice or saliva samples were positive for Helicobacter sp. However, Helicobacter sp. DNA was detected in dental plaque from two dolphins, suggesting the oral cavity might be a reservoir of this bacterium.