Abstract: A novel SVD based gray-level digital watermarking algorithm is presented.In this algorithm,data from high bit to low bit of decomposed bit planes of the gray-level watermark image are embedded respectively into corresponding singular values from large to small obtained by SVD of sub blocks of the original image.And that the revision for resistance against brightness-and-contrast adjustment is adopted makes that this algorithm has the robustness against brightness-and-contrast adjustment attack.The experimental results show that this algorithm has fine transparency of the embedded watermark and has extremely strong robustness against brightness-and-contrast adjustment attack,and it has as well strong robustness against other common image-processing attacks such as image smoothing,noise adding,color dithering,and JPEG-compression.