A display device includes a display panel, a variable gate clock generator and a gate driver. The display panel includes a plurality of pixels coupled to a plurality of data lines and a plurality of gate lines, respectively. The variable gate clock generator generates a first variable gate clock signal and a second variable gate clock signal having respective duty ratios that are varied depending on a brightness of a frame image. The gate driver generates a plurality of gate driving signals for driving the gate lines in response to the first and second variable gate clock signals.