Acid orange 7-pillared layered double hydroxide (AO7-LDH) has been prepared by coprecipitation and studied with both experimental characterizations and theoretical calculations. XRD patterns indicate that the product has the typical intercalated structure of LDHs with a gallery height of 1.79 nm, showing that a kind of large anion has been intercalated into the interlayer space of the LDH. Infrared spectrum of AO7-LDH shows that the product has the characteristic absorption bands of both azo and hydrazone forms of AO7 anion, as well as the Mg-O and Al-O vibrations of LDH layers, well convincing the intercalation of AO7 anions successful. TG-DTA curves demonstrate clearly that the thermal stability of AO7 can be enhanced by nearly 130 degrees C when it is intercalated into the LDH layers. According to the size of AO7 anion (1.25-1.27 nm) obtained by density functional calculations of quantum chemistry at the level of B3LYP/6-31G(d,p), the AO7 anions should be vertical-arranging in the interlayer space, forming a interdigitated structure. (c) 2007 Elsevier B.V. All rights reserved.