The objective of this research is to propose a suitable watermarking method for the dot matrix hologram to display 3D image. Error diffusion and pseudo random number are used to embed watermark into halftone image, and then watermarked image is integrated into a 3D holographic image. After outputting the encoded hologram, this holographic image is captured and the watermark is extracted by digital image processing. The result shows that it is feasible to embed watermark in the 3D holographic image. Watermarked 3D-hologram possesses both artistic quality, and anti-counterfeit function.