A method and device are provided for adjusting brightness of an optical touch panel. The optical touch panel comprises a microprocessor, a display module including a back light source, and an optical position detection device including optical transmitting devices and optical receiving devices. The method comprises detecting, via the optical receiving devices, a current ambient light level on the display module. The method further comprises generating, via the optical receiving devices, a current ambient light level signal indicative of the current ambient light level and transmitting the current ambient light level signal to the microprocessor. Furthermore, the method comprises adjusting, via the microprocessor, brightness of the back light source based on the current ambient light level signal.