This paper presents a watermarking method for the copyright protection and the prevention of illegal copying of mobile 3D contents. The proposed method embeds the copyright information and user's phone number into the spatial and encryption domains of the mobile animation data using the Buyer-Seller watermarking protocol. In addition, a user operation key is also inserted, so only the authorized user can play the 3D animation game on the mobile device. The proposed method was implemented using a mobile animation tool, and experimental results verified that the proposed method was capable of copyright protection and preventing illegal copying, as the watermarks were also accurately extracted in the case of geometrical attacks, such as noise addition, data accuracy variation, and data up/down scaling.