In this paper we propose an algorithm to develop an intelligent perceptual shaping function based on Genetic Programming (GP) in DCT domain. In digital image watermarking, robustness and imperceptibility compete with each other. In this paper we applied GP to make a trade off between these two characteristics. Here, the original image is divided into 8×8 non-overlapping blocks and the DCT coefficients in each block are sorted by means of zigzag. One AC coefficient in each block is changed according to a perceptual shaping function. This perceptual shaping function is obtained from the GP core and is dependent on average of all block coefficients and the related AC coefficient. The experimental results show that this proposed algorithm is robust against some digital image attacks such as low pass filtering, median filtering and JPEG compression. In addition the improvement in watermarked image quality also is achieved.