The invention discloses an adaptive image sharpening method for generating a sharpened image area corresponding to an original image area. The original image area includes a plurality of original pixel values. The method includes blurring the original image area to generate a plurality of blurred pixel values corresponding to the plurality of original pixel values respectively, calculating a plurality of characteristic values corresponding to the plurality of original pixel values respectively, statistically analyzing the plurality of characteristic values to generate a plurality of weighting values corresponding to the plurality of original pixel values respectively, and generating a plurality of sharpened pixel values according to the plurality of original pixel values, the plurality of blurred pixel values, and the plurality of weighting values. The plurality of sharpened pixel values constitutes the sharpened image area.