To obtain an antibacterial agent for Helicobacter pylori contributing to diseases involved in the upper digestive tracts such as gastric ulcer.

This antibacterial agent contains at least one substance selected from synthetic aluminum silicate, natural aluminum silicate, dried aluminum hydroxide get, Antipollon HT and Takallophane and at least one kind of agent selected from β-lactam-based antibiotics, macrolide-based antibiotics, nitroimidazole-based antibacterial agents, proton pump inhibitors and H2-receptor antagonistic agents. This antibacterial agent can entirely avoid side effects on the nerve system inherent in bismuth preparations as the conventional effective agent.