Keggin-type heteropoly acids (HPAs) were immobilized in the unique network structure of resorcinol-formaldehyde (RF)-derived carbon gels. Two methods were employed for immobilization, one by impregnating 12-tungstophosphoric acid (PW12) in a wet RF hydrogel followed by drying and carbonization of the support, and the other by synthesizing 12-molybdophosphoric acid in a slurry mixture of carbon gel particles and deionized water. It was found that significant amounts of the acids could be immobilized to carbon gel supports by both methods, and large amounts of the acids remained in the carbon supports even after long-term hot water extraction. Moreover, the obtained complexes were found to show catalysis in the synthesis of methyl-tert-butyl ether from methyl alcohol and tert-butyl alcohol, indicating that they could be practically used as solid acid catalysts in various reactions which involve water. (C) 2003 Elsevier B.V. All rights reserved.