The present invention discloses an adaptively de-blocking circuit and associated method. A mean is derived according to the neighboring pixels surrounding a central pixel of an image. A blending factor is determined according to a flatness of the image. An updated pixel value of the central pixel is determined by blending the original pixel value of the central pixel and the mean according to the blending factor. Finally, alternatively output the updated pixel value and the original pixel value of the central pixel in response to a block border signal.