Gold nanoparticles and nanostructures were electrodeposited on transparent ITO electrodes in the presence of l-cysteine. When the deposition potential was shifted from −0.5V (vs. Ag|AgCl) to 0.0V (deposition time: 60s), the gold nanoparticles changed from spheres to larger and bumpy structures, resulting in a redshift of the absorption peak based on localized surface plasmon resonance (LSPR) from 630nm to 710nm. Prolonged deposition at −0.5V increased the size as well as the absorption and scattering of the spherical nanoparticles. At 0.0V, elongated deposition increased the size of the bumpy nanoparticles, and finally yielded more complicated three-dimensional structures including dendritic structures, which gave low scattering and intense absorption. The electrodeposited gold nanoparticles were applied to a LSPR sensor for refractive index with controllable working wavelength and sensitivity.