Four Mg/Al type hydrotalcite-like materials (HT) with different interlayer anions were synthesized by a co-precipitation method under the condition of Mg/Al = 2.5, and their pH buffer action was investigated. Slurries of these HTs each showed a constant pH due to the buffer action, with equilibrium pHs in the following order: Mg-Al-SO42-HT (pH 9.0)> Mg-Al-CO32- HT (pH 8.5)> Mg-Al-NO3-HT (pH 8.0)> Mg-Al-Cl-HT (pH 7.6). The equilibrium pHs of Mg-Al-SO42-HT and Mg-Al-CO32-HT, in which divalent anions are intercalated as exchangeable anions, are higher than those of Mg-Al-Cl-HT and Mg-Al-NO3- HT, which have rnonovalent anions in the HT structure. This phenomenon is mainly caused by the consumption of H+ in aqueous solution with SO42- or CO32- released from HT. The slightly higher equilibrium pH of Mg-Al-NO3-HT compared with Mg-Al-Cl-HT is thought to be based on the difference in the amount of OH- in the FIT interlayer. From these results, it is clear that the pH buffer action of the layered double hydroxide varies with the kind and amount of anion captured in HT.