Potentially fatal chemotherapy (CT)-related gastrorrhagia and gastric perforation in patients with gastric lymphoma present difficult problems to doctors. We retrospectively analyzed 54 patients with ulcerative gastric diffuse large B-cell lymphoma (G-DLBCL) to compare the safety and efficacy of low-dose pre-phase CT before 4-6 cycles of conventional-dose CT (n = 28) with 4-6 cycles of conventional-dose CT (n = 26) between October 2005 and August 2014. Patients who received low-dose pre-phase before conventional-dose CT showed a lower gastrorrhagia or gastric perforation rate (0% vs. 15.4%, p = 0.047) and higher complete response (CR) rate (78.6% vs. 46.2%, p = 0.023) and 5-year progression-free survival (PFS) rate (63% vs. 31%, p = 0.021) than patients who received conventional-dose CT alone. Our study suggests that low-dose pre-phase therapy before conventional-dose CT provides a safe and effective method for ulcerative G-DLBCL.