A timing controller is provided. The timing controller comprises a data analyzer, a gain processor, an operator unit and an original gamma voltage generator. The present invention utilizes the data analyzer to analyze a gray level distribution of video data, and then the gain processor selects a gain value. The operator unit converts an original gamma voltage produced by the original gamma voltage generator into an actual gamma voltage according to the gain value. Therefore, the present invention adaptively adjusts the gamma voltage according to the gray level distribution of the video data for increasing display quality.