An image processing circuit and a method thereof are provided herein. The image processing circuit has a first scaling circuit, one or more line buffers, a first sharpness circuit, a second scaling circuit, and a second sharpness circuit. The first scaling circuit enlarges an input image along a first direction to generate a first enlarged image. The one or more line buffers temporarily store the pixel values of a plurality of pixel rows of the first enlarged image. The first sharpness circuit vertically sharpens the first enlarged image to generate a first sharpened image. The second scaling circuit enlarges the first sharpened image along a second direction to generate a second enlarged image. The second sharpness circuit horizontally sharpens the second enlarged image to generate a second sharpened image. Accordingly, it is possible to use the one or more line buffers having shorter data lengths to perform the vertical sharpening.