The prevalence of Helicobacter pylori (HP) were studied in 117 subjects with no gross findings whose stomach age was equal to its chronological age. HP was detected by culture. The prevalence of HP significantly was higher in thirties and forties than other ages, and in C3 and O1 groups than other groups. Most of forties and fifties belonged to C3 or O1 groups. Histologically, HP infection was significantly frequent in the gastric mucosa with advancing inflammation. These findings suggest that HP infects in early middle age, causes the destruction and atrophy of gastric mucosa and disappears with ageing and chronological expansion of mucosal atrophy. We consider that HP infection may play a causative role of the aging process of the stomach.