Background. Proton pump inhibitor and histamine-2 receptor antagonist can prevent aspirin-related ulcers/erosions but few studies compare the efficacy of these two agents. Aims. We evaluated the efficacy of omeprazole and famotidine in preventing recurrent ulcers/erosions in low-dose aspirin users. Methods. The 24-week clinical outcomes of the patients using low-dose aspirin for cardiovascular protection with a history of ulcers/erosions and cotherapy of omeprazole or famotidine were retrospectively reviewed. The incidence of gastrointestinal symptoms, recurrent ulcers/erosions, erosive esophagitis, gastrointestinal bleeding, and thromboembolic events was analyzed. Results. A total of 104 patients (famotidine group, 49 patients; omeprazole group, 55 patients) were evaluated. Famotidine group had more gastrointestinal symptoms episodes than omeprazole group (46.9% versus 23.6%, P = 0.01). Fifteen famotidine group patients and 5 omeprazole group patients had recurrent ulcers/erosions (30.6% versus 9.1%, P = 0.005). Lanza scale was significantly lower in omeprazole group than in famotidine group (1.2 ± 0.7 versus 1.7 ± 1.1, P = 0.008). Only 1 famotidine group patient had ulcer bleeding. The incidences of erosive esophagitis and thromboembolic events were comparable between both groups. Conclusions. Omeprazole was superior to famotidine with less gastrointestinal symptoms and recurrent ulcers/erosions in patients using 24-week low-dose aspirin. The risk of erosive esophagitis, gastrointestinal bleeding, and thromboembolic events was similar between both groups.