Gold/silver nanoparticles were trapped at the oil/water interface of oil droplets dispersed in water. The metallic nanoparticles were self-assembled into a uniform two-dimensional large array structure through the aggregation and coalescence of the nanoparticle-covered oil droplets. The plasmon resonance of the array structure was tunable and a surface-enhanced Raman scattering measurement was performed with the silver nanoparticle array. The enhancement factor was similar to 10(5) and enhanced Raman signals were observed over the whole array (greater than or similar to cm(2)) with high reproducibility, which is an advantage of a self-assembly method using a liquid/liquid interface. (C) 2016 The Japan Society of Applied Physics