This paper describes a simple and facile method for the synthesis of Ag/Au bimetallic hollow and porous nanoshells (HPNSs) with controllable porosity, using polycrystalline Ag nanoparticles as starting templates. The optical and catalytic properties of the HPNSs can be easily tuned by using hydrogen peroxide as a mild etchant to controllably dissolve Ag atoms from the precursor Ag/Au bimetallic hollow nanoshells (NSs). The surface plasmon bands of the HPNSs can be easily tuned from the visible to the near infrared (NIR) region. As a model reaction to evaluate the catalytic activity of the HPNSs, we chose the reduction of p-nitrophenol by NaBH₄ to afford p-aminophenol. The porous NSs exhibit higher catalytic activity than non-porous NSs even though the latter have higher Au/Ag ratios than the former. Although the composition (Au/Ag ratio) may have some effect, the morphology (porosity) of the HPNSs plays the most important role in the catalysis. The as-synthesized plasmonic HPNSs, due to their facile aqueous-phase preparation, tunable optical properties (in the visible and NIR windows), and unique porous hollow structures, have promising potential applications in various fields ranging from biosensing, nanomedicine (drug/gene delivery, cancer theranostics, etc.), to catalysis and solar cells.