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), €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ(Mg a Zn b ) 1-x Al x (OH) 2 (A n- ) x/n · mH 2 O€ƒ€ƒ€ƒ€ƒ€ƒ(1) wherein A n- is CO 3 2- , SO 4 2- 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.
