This invention relates to a clock with intelligent backlight device comprising a casing, a power supply, timing components, a printed circuit board, time setting buttons and so forth. The power supply is in the form of dry batteries placed inside the battery box of the casing. Inside the casing there are a backlight device and a backlight source. The backlight device is disposed at the back of the timing components, and the backlight source is disposed at the back of the backlight device. The printed circuit board is installed with integrated circuits, the first output thereof drives and controls the timing components, the input thereof connects to the time setting buttons, while the second output thereof drives and controls the backlight source through a photosensitive resistor and an electronic switch in serial connection. The present invention is powered by dry batteries and is operated by low voltage and current. Further, it can automatically switch on or off the backlight in response to changes in the luminosity of the surroundings. It is convenient to use, and it can also prolong battery life span so as to save resources.