Poly(2‐ethylaniline) chains were synthesized within the three‐dimensional channels of dehydrated zeolites X and Y. The Na‐ and acidic forms of the zeolite hosts were loaded with the monomer from hexane solution, which was subsequently oxidized with aqueous (NH4)2S2O8. The steric demands for the polymerization are illustrted by the inability of the polymer to form in the one‐dimensional channel system of mordenite. Since protons are not necessary for the polymerization to occur, the polymer is formed in the acid form of the zeolites as well as in the Na‐forms. Polymerization occurs also at the outer surfaces of the zeolite crystals. The external polymer can be removed with chloroform after it was converted to the soluble base form. The intrazeolite polymer chain length peaks at about 0.1 &mgr;m (determined from gel permeation chromatography), and is substantially greater than that obtained in bulk polymerizations.