A chaos-based watermarking algorithm in DCT-domain for still images is proposed, and the algorithm is a blind watermarking scheme. Firstly, the watermark is scrambled by one chaos map with keys; Secondly, the scrambled watermark is embedded into the least signification bits (LSB) of the quantized DCT coefficients, which the watermark embedded into are determined by another map with another keys. Only the ones who knows the keys can extract the watermark from the stego-image, so it is security. experimental results have confirmed that this new scheme has high fidelity and is highly robust against geometric attacks and signal processing operations.