An apparatus to improve an image sharpness and a method thereof which can improve the image sharpness of an image through an adaptive operation of the apparatus according to resolutions of input/output video signals and an emphasis of edge portions of the image. The apparatus to improve the image sharpness includes a plurality of band pass filters to respectively extract preset different frequency bands from a first video signal converted and inputted according to a video format of a display device, a filter selection part to select and operate at least one of the plurality of band pass filters, at least one first differentiator to differentiate video signals outputted from the selected band pass filters, at least one second differentiator to second-differentiate the differentiated video signals outputted from the first differentiators, at least one amplifier to amplify the second-differentiated video signals of the at least one second differentiator according to a preset amplification factor and to output a second video signal, and an adder to invert the second video signal, and adding the inverted second video signal to the first video signal to output an added video signal as the output video signal.