A liquid-crystal display device and a driving method thereof are disclosed. The driving method of the liquid-crystal display device comprises: generating first and second power supply voltages; generating gamma-compensated voltages based on the first and second power supply voltages; converting data of an input image to the gamma-compensated voltages to output data voltages; distributing, by a multiplexer, the data voltages output from the data driver to a plurality of data lines; and varying at least one of the first and second power supply voltages at a given time interval.