Disclosed is an electrolyte for electrochromic devices, which includes a eutectic mixture comprising: (a) a compound having an acidic functional group and basic functional group; and (b) an ionizable lithium salt. An electrochromic device using the same electrolyte is also disclosed. Because the electrochromic device uses the electrolyte comprising the eutectic mixture, which is cost-efficient and has excellent thermal and chemical stability, there are no problems related with evaporation and exhaustion as well as flammability of electrolyte. Additionally, it is possible to minimize side reactions with constitutional elements of an electrochromic device and electrolyte, thereby improving the safety. Further, it is also possible to improve the quality of an electrochromic device by virtue of a broad electrochemical window and high electroconductivity of the eutectic mixture.