Helicobacter pylori (H. pylori) is a major causative agent of atrophic gastritis and peptic ulcer as well as associated with gastric carcinogenesis. The bacteria not only can persistently colonize the stomach by evading the immune system of the host, but also has antibacterial drug resistance. Thus, the need for alternative medicine to effectively eradicate the bacteria has become more important. Phytochemicals from crucifer vegetables are well-known alternative medicines as antibacterial substances. Among various crucifer vegetables, a turnip (Brassica rapa L.), in the family Brassicaceae, was evaluated in the present study because of its popularity on ethnopharmacology and the advantage of long-term storage after harvest. The evaluation was done by colony formation unit calculation, urease activity test, anti-H. pylori IgG titer measurement, proinflammatory cytokine measurement, and histopathological assessment after sacrificing the infected mouse model. Among the experimental groups, the group treated with a high dose of myrosinase-reacted turnip roots exhibited a distinctive anti-H. pylori activities, such as reduced bacterial colonization and increased anti-H. pylori IgG titer. Thus, the present study suggests a turnip as a new functional dietary regimen for the treatment of H. pylori infection. Furthermore, the present study can be utilized as a basis for the development of safe and effective drugs for other infectious alimentary diseases.