An in situ sacrificial oxidative template route has been developed for the bulk synthesis of two-dimensional polyaniline nanostructures, such as nanorings and flat hollow capsules. In the reaction system, VOPO4 center dot 2H(2)O nanoplates formed spontaneously in V2O5/H2O2/H3PO4 mixture can serve as both oxidant and sacrificial template for the chemical oxidative polymerization of aniline. The synthetic parameters, such as reaction times, the concentrations of H3PO4, and types of the oxidants on the I morphologies, sizes, and molecular structures of polyaniline nanostructures have been investigated. The time-dependent experiments reveal that VOPO4 center dot 2H(2)O nanoplate is etched gradually with the polymerization reaction proceeding. The concentration of H3PO4 can adjust the polymerization rate of aniline as well as the etching rate of VOPO4 center dot H2O, which is critical for controlled synthesis of polyaniline nanorings and flat hollow capsules. The sacrificial oxidative template approach can be extended to synthesize two-dimensional polypyrrole nanostructures.