Watermarking is a potential method for copyright protection and multimedia data authentication in the internet. The watermarking process can be considered as a communication task. In this paper, a novel watermarking scheme using code division multiple access (CDMA) modulation is proposed to achieve a superior performance in terms of robustness and imperceptibility. In the proposed scheme, every three watermark bits are modulated into a five bit MCDMA code. Then the MCDMA code is concealed in the coefficients of a DCT block. To demonstrate the efficiency of the proposed scheme, simulations under various conditions are conducted. The empirical results show that our proposed scheme can stand up against most common attacks including JPEG compression, rotating, resizing, cropping, mosaicking, noising and blurring etc.