A device for measuring an optical property of a liquid crystal display is provided. The device has a light source providing a light, a first polarizer pervious to the light, a second polarizer pervious to the light, a detector receiving the light, and a calculating module. The first polarizer and the second polarizer are mounted between the light source and the detector, a first transmittance spectrum is obtained while the liquid crystal display is mounted between the first polarizer and the second polarizer, and a second transmittance spectrum is obtained while the liquid crystal display is mounted between the detector and the first and second polarizers.