A modulation of electrochromic and electrofluorescent properties in one device was possible by coupling of 9-methylanthracene polymer (PMAn) having blue light emission under 390 nm light excitation, and poly(3,4-ethylenedioxythiophene) (PEDOT) having blue to transparent electrochromism (EC). The different redox states between electrofluorescent (EF) and electrochromic (EC) polymer films could provide the electrochemically switchable color and fluorescence in one device. Alternative EF and EC switching between a blue light/dark and colorless/blue color was achieved from the device with reversible switching within 3.5 s by the potential application under perpendicular to 2 V.