The first localized surface plasmon resonance (LSPR)-based multicolor electrochromic device with five reversible optical states is demonstrated. In this device, the size of deposited silver nanoparticles is electrochemically controlled by using a voltage-step method in which two different voltages are applied successively. The electrochemically size-controlled silver nanoparticles enable a reversible multiple-color change by a shift of the LSPR band.