Polyaniline (PANI) zeolite composites have been prepared by oxidative polymerization of anilinein the presence of zeolite 13X, producing composite materials with PANI/zeolite weight ratios from about 0.5 to 55. The DC conductivity of the composite materials decreased exponentially with zeolite weight fraction. Pure PANI was paramagnetic while the PANI/zeolite complexes with weight ratios larger than 20 showed an appreciable antiferromagnetic component as indicated by temperature dependence of their electron spin resonance spectra. This novel antiferromagnetism is speculated to arise from pi -dimer pairing of PANI chain layers stacking on the zeolite particle surface.