Development of new methods for producing large-area nanocrystals with specific shapes is crucial for advancements in various fields. In this study, submillimetersized sheet-structured gold crystals with nanoscale thicknesses were fabricated by chemical reduction of HAuCl4 in the presence of long-chain amidoamine-derived surfactants (CnAOH; n = 12, 14, 16, or 18) in aqueous solutions. Using the C18AOH system at 30 degrees C, large-area sheet-structured crystals with widths of similar to 100 mu m and thicknesses of 30 nm were effectively obtained at the air/water interface. The crystal size depended on the temperature and the alkyl-chain length of the surfactant. An investigation of the relationship between the crystal growth and the interfacial properties of CnAOH revealed that large-area crystals were obtained when densely packed molecular layers of long-chain CnAOH were formed at the air/water interface. The interfacial molecular layer of C18AOH showed most effective soft-templating effect and contributed in promoting the growth of sheet-structured gold crystals.