First, the various attitudes towards homosexuality among Confucianism, Christianity and ancient Greek culture are considered. Distinguished from the Christian harsh repulsion and the Greek slight encouragement, Confucianism has been guardedly tolerant of homosexuality and judged homosexuals according to their personal moral behavior. To reveal the deep reasons for the distinction between Confucianism and Christianity on this issue, the paper examines the differences in thinking between the Western dichotomy and the Confucian genesis by the co-opposites of yin-yang. Confucianism explains homosexuality as one of the possible results of the yin-yang process. It is thereby a natural phenomenon, not an evil thing. However, it is due to this understanding that Confucianism cannot advocate the legalization of homosexual marriage, because a union between homosexuals does not belong to a true yin-yang means of combination and production. To treat it legitimately as being the same as a marriage between heterosexuals could lead to consequences that would be unfavorable to the longevity of human communities, which include, for instance, opening up the possibility of group marriage; hurting innocent people; and leading those who do not have a definite sexual tendency to make a homosexual decision. The third part of the paper refers to the Confucian saying cited by Anthony Kennedy, the Chief Justice of the Supreme Court of the USA, in his statement on the ruling on same-sex marriage, and shows that his citation was inaccurate, but its content was not far from the original meaning of Confucius’ saying. Further, the conflict between Kennedy’s basic thinking and the Confucian thought demonstrated in the citation and its context is exposed.