The present invention discloses a measurement device for measuring the gray-to-gray response time. The measurement device is capable of precisely measuring the gray-to-gray response time of an LCD. According to a video signal comprising a synchronous message, the measurement device obtains the initial time and the final time of each gray-to-gray response time interval in the transition of LCD luminance, so as to achieve synchronous measurement of the LCD gray-to-gray response time.