Objective. To evaluate the effect of eradication of Helicobacter pylori (H. pylori) on the progression of dementia in Alzheimer’s disease (AD) patients with peptic ulcer. Methods. Participants with the diagnosis of AD and peptic ulcer were recruited between 2001 and 2008. We examined the association between eradication of H. pylori and the progression of AD using the multiple regression models. Medication shift from Donepezil, Rivastgmine, and Galantamine to Mematine is defined as progression of dementia according to the insurance of National Health Insurance (NHI) under expert review. Results. Among the 30142 AD patients with peptic ulcers, the ratio of medication shift in AD patients with peptic ulcers is 79.95%. There were significant lower incidence comorbidities (diabetes mellitus, hypertension, cerebrovascular disease, coronary artery disease, congestive heart failure and hyperlipidemia) in patients with H. pylori eradication as compared with no H. pylori eradication. Eradication of H. pylori was associated with a decreased risk of AD progression (odds ratio [OR] 0.35 [0.23–0.52]) as compared with no H. pylori eradication, which was not modified by comorbidities. Conclusions. Eradication of H. pylori was associated with a decreased progression of dementia as compared to no eradication of H. pylori in AD patients with peptic ulcers.