Tailoring optical response using periodic nanostructures is one of the key issues in the current research on functional composite materials. [1][2][3][4][5] The anomalous light transmission through metallic films that have a regular array of submicrometer holes [3][4][5][6] has stimulated much interest. This interest stems from both the underlying physics and also the perceived potential for applications in nanophotonics, [7] quantum-information processing, [8] nanolithography, [9] and surface-enhanced Raman scattering.[10]Extraordinary transmission of light through an optically opaque metal film perforated with a 2D array of subwavelength holes was first reported by Ebbesen et al. [5] This unusual phenomenon can be understood as a result of diffractive coupling to evanescent surface plasmon polaritons (SPPs) that leads to a strong concentration of light at the metal surface, which then weakly tunnels through the holes in the film, reradiating by the inverse process on the exit side. [4,[11][12][13] In order to explore the SPP properties of microstructured metal films, extensive efforts have been made to study their spectral response and dependence on geometrical parameters, such as the type of lattice symmetry, metal film thickness, and adjacent dielectric media. [14] Recent studies show that the hole shape has a significant effect on the optical transmission. [15][16][17][18][19] Nearly all the metallic films studied have been on a flat substrate and the hole arrays were made using focused ion-beam milling, [5,15,17,19] and electron-beam lithography [8] or interferometric lithography combined with reactive ion etching. [16,18] Here we use nanosphere lithography [20] as the sample production technique. This approach has several advantages over the conventional lithographic and machining techniques, including the relative ease of casting large, high-quality, ordered nanomaterials and the low cost of implementation. Ordered arrays of gold half shells and nanocaps have been constructed by controlled gold vapor deposition with thicknesses less than 20 nm by using a 2D colloidal crystal (CC) as a substrate. [21,22] Baumberg's group has fabricated metallic nanocavity arrays by electrodeposition within the pores of CC templates and observed the excitation of the SPPs in metallic cavities that led to rich features in reflectivity spectra.[23] Very recently, Landström et al. have shown that the transmission spectra through a metal film formed on a 2D CC substrate are quite similar to those observed through subwavelength hole arrays in metal films. [24] In this communication, we report a study on the infrared transmission properties of gold films patterned on 2D CCs. The fabricated metallodielectric structures have a strong surface corrugation as well as a 2D periodic pore array. We show that the SPPs on these curved surfaces display unusual dispersion properties, compared to those of metal films on flat substrates studied before. The dielectric property of the template spheres is also found to have a substantial effect o...