Xenotransplantation research raises a number of ethical issues, such as a possible outbreak of new/zoonotic infection, violating an individual’s privacy, and harm to the animals (especially to onhuman primates) that are used in experiments. Since 2004, xenotransplantation researchers and doctors associated with the Xenotransplantation Research Center (XRC) have been receiving education related to the ethical issues involved in xenotransplantation research at least twice per year. Learners’ attitudes toward xenotransplantation have been investigated three times: in 2004, 2007, and 2010. The objective of this study was to discover the changes in learners’ attitudes toward xenotransplantation issues and to identify the best form of ethics education for xenotransplantation researchers. The Ethics Education for Researchers provided to XRC associates since 2005 has involved seven units on laws and regulations, nine units on general ethical issues, five units on the ethics of animal research, and ten units on laboratory management and ethics. To the question concerning the justifiability of xenotransplantation research, 100 percent of respondents answered “Yes, it is justifiable” in 2004. However, the proportion of positive responses decreased to 90.9% in 2007 and 86.2% in 2009. The proportion of respondents who considered “the risk of zoonosis” and “lack of established legal framework” as top-priority projects has increased. The preferred educational method was “case-based study.” After receiving the Ethics Education for Researchers, researchers tended to be more conscious of the ethical issues raised by xenotransplantation research. This study suggests a need for mandatory ethics education for xenotransplantation researchers using a variety of educational methods.