Heterogeneous alkene epoxidation catalysts prepared by immobilization of species derived from MoO2(acac)(2) on two polymers, a polystyrene N-hydroxypropyl aminomethylpyridine resin and a polybenzimidazole resin, are known to behave differently. The two catalyst species have now been characterized extensively in terms of both the molecular structure of the Mo(VI) centers and the resin morphologies, and significant differences have been demonstrated in both aspects. Molecular structural characterization has involved elemental analysis and FTIR, electronic, and X-ray photoelectron spectroscopies, together with EXAFS analysis and associated modeling. Morphological studies have employed high-resolution transmission electron microscopy with Mo mapping, N-2 sorption, and Hg intrusion porosimetry and solvent imbibition measurements. The differences observed account for the observed variation in catalytic behavior, and these structural and morphological differences are discussed in detail.