A novel image watermarking algorithm was designed by taking the advantage that ridgelet transform domain is a more suitable representation of image’s linear outline edge features than wavelet transform. Firstly,the image was divided into blocks,and each block was transformed by finite ridgelet transformation. Secondly,the watermark was spread spectrum modulated by two zero mean and uncorrelated random sequences. At last,the modulated watermark was additively embedded in the high frequency coefficients of ridgelet transform domain. Experiment results show that the proposed algorithm can not only resist common attacks such as compression,noise,filtering and cropping,but also resist image gray enhancement and weakened attack. The comparison with wavelet transform domain watermarking algorithm also shows the advantages of the algorithm.