Disclosed is a therapeutic agent for ulcer, which comprises a composite hydrotalciteparticle as an active ingredient, wherein the composite hydrotalcite particlecomprises a hydrotalcite particle and zinc contained in the hydrotalcite particlein the form of a solid solution, has an excellent therapeutic effect on pepticulcer, and can also act as a Zn-supplying agent. Specifically, a composite hydrotalciteparticle represented by formula (1) is used as an active ingredient. The compositehydrotalcite particle is produced by adding a small quantity of Zn to a hydrotalciteparticle in the form of a solid solution. (Mg
