A gastric ulcer therapeutic agent comprising as an active ingredient a composite hydroxide of a hydrotalcite and an aluminum hydroxide compound, which composite hydroxide is represented by the formula (1),Mg1-xAlx(OH)2+x-ny(An-)y(H2O)m (1),wherein An-represents an anion, n represents a valence of the anion in the range of 1 to 4, x is in the range of 0.34<；x<；0.7, y is in the range of 0<；y<；0.8, and m is in the range of 0<；m<；4.
