In this study, the rapid synthesis of small, uniform gold nanoparticles (NPs) has been achieved using an electrochemical technique with an alkaline solution. Gold NPs with high purity and uniformity can be synthesized by adding sodium hydroxide to the electrolyte, which can cause the NP radius to reduce dramatically from 30 nm to 5 nm. The whole reaction time is 5 minutes. The morphology, purity, and optical properties of various NPs were confirmed by energy-dispersive X-ray spectroscopy, transmission electron microscopy, and ultraviolet-visible spectroscopy. The wavelength of the absorption spectrum is approximately 520 nm when the radius of NPs is approximately 5 nm. (C) 2016 The Electrochemical Society. All rights reserved.