An agent for treating ulcer containing, as an effective component, a particulate composite hydrotalcite obtained by solidly dissolving a small amount of zinc in the particulate hydrotalcite, exhibiting excellent effect for treating the peptic ulcer and, further, working as a Zn-supplying agent. The agent for treating the ulcer is represented by the following formula (1),(MgaZnb)1-xAlx(OH)2(An−)x/n.mH2O (1)wherein An− is CO32−, SO42− or Cl−, n is 1 or 2, and x, a, b and m are values that satisfy the following conditions,0.18≦x≦0.4, 0.1≦a<；1, 0<；b≦0.5, 0≦m<；1.
