Helicobacter pylori (H. pylorii) changes from a spiral form to coccoid by the aggravation of its surrounding environment. It was believed that the coccoid H. pylori indicated to be dying or becoming dormant. However, the implication of coccoid formation, itself, has not yet been elucidated. In this study, both the ultrastructural changes and the localization of the intracellular DNA were observed during coccoid formation in H. pylori. Some coccoid forms were observed to adhere to each other during transformation from the spiral form. The DNA and Cag A in each bacterium were detected at the boundary area of the aggregate, and then mixed in one new coccoid bacterium formed from the syncytium by plural bacteria. This type of coccoid formation was thought to be a transfer phenomenon of intracellular genetic proteins into neighbor organisms. In other words, the coccoid formation of H. pylori means not only the dying or the dormant condition but also a horizontal gene transfer processes with a positive significance for species-preservation under environmental stress.