An inorganic polymeric hydrogel, which is formed irreversibly in water through interaction between K2PdIICl4 and K4FeII(CN)6, is synthesized. The palladium nanostructures take the form of three-dimensional (3D) networks and are obtained in a facile manner by simple reduction of the hydrogel using NaBH4. The size, morphology, and surface composition of these 3D palladium networks are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), selected-area electron diffraction (SAED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties are investigated in detail by cyclic voltammetry, chronoamperometry, and CO stripping tests. Such 3D nanostructures exhibit a large electroactive surface area, excellent electrochemical stability, and high electrocatalytic activity toward electrooxidation of formic acid.