Amorphous inorganic ion exchanger zirconium phosphate and its phenyl derivative, zirconium phenyl phosphonate have been prepared and characterised. The protons of the hydroxyl groups are found to be the active sites. Such materials indicate good potential for Bronsted-acid catalysis. Esterification has been studied as a model reaction wherein ethyl acetate has been prepared. It has been observed that zirconium phenyl phosphonate behaves as a better Bronsted acid catalyst as compared to zirconium phosphate.