Abstract Oxidative polymerization of aniline was performed using both CuZr(PO 4) 2 (CuZrP) and Zr[O 3P(CH 2) 3COOH] 0.75(O 3POH) 1.25 [ZrP(bt) 0.75(OH) 1.25] as catalysts. In the CuZrP reaction, the non-conducting emeraldine base form of polyaniline (PANI) formed on the surfaces of the phosphate microcrystals. When exposed to HCl, the solid CuZrP·PANI turned from violet to green, indicating formation of a protonated conducting polymer. In the reaction with the mixed phosphonate ZrP(bt) 0.75(OH) 1.25, a violet product also formed, with the interlayer spacing of the solid increasing significantly, indicating polymerization within the interlamellar region. The solid product did not react with HCl. IR spectra indicated a slightly different form of PANI included in the phosphonate than on the surface of CuZrP.