Embedding a personal identifier as a watermark to Java classfile is effective in order to protect copyrights of them. Monden et al. proposed watermarking scheme that embeds arbitrary character sequence to the target method in a Java classfiles. But the scheme can be only used to embed the same watermark to each user's classfiles. Therefore, if we apply this scheme for embedding each user's personal identifier, the watermarks can be specified by comparing two or more users' Java classfiles. In this paper solve the problem by using "Classfiles Obfuscation" which is our obfuscation scheme for Java sourcecodes. By the scheme, we distribute all the methods among the all the Java classfiles at random. Evrey user's Java classfiles will have different structures respectively by appling "Clasfiles Obfuscation". As the result, to specify watermark by compareing classfiles will be difficult.