A method and an apparatus for compensating a black level are provided, in which an image signal processor converts an input image signal into an image signal at YUV color coordinates so that the image signal at the YUV color coordinates is in a first signal range, and a black level compensator compensates a Y component of the image signal at the YUV color coordinates so that the Y component of the image signal at the YUV color coordinates are in a second signal range narrower than the first signal range or maintains the Y component of the image signal at the YUV color coordinates in the first signal range, according to a type of an external image output device.