In conventional spread spectrum watermarking schemes, random sequences are used for the modulation of watermark information. However, because of the mutual interference among those sequences, it requires complicated removal operation to improve the performance. In this paper, we propose an efficient spread spectrum watermarking scheme by introducing the CDMA technique at the modulation of watermark information. In order to control the energy assigned to spread spectrum sequences, we propose a coded method that encodes watermark information into a constant weight codeword. If the weight and its code-length are properly selected, the performance of the method could outperform the conventional methods. © 2013 Springer-Verlag.