The purpose of this paper is to clarify the difference between Korean Neo Confucianism and Japanese Neo Confucianism. From the beginning of the 12th century, Zen monks introduced the Neo Confucianism of Southern Song to Japan. Seika Fujiwara, the founder of Japanese Neo Confucianism, had compromised Neo Confucianism, Yangmig theory, and Buddhism. Since the Edo period, Ansai Yamazaki has been evaluated as the most accurate scholar on Yi Toegye in Japan. What impressed Ansai Yamazaki a lot about Yi Toegye was Yi Toegye’s attitude toward Chu Hsi. Ansai Yamazaki also pointed out the limitations of Yi Toegye. He criticized Yi Toegye for not being able to interpret the origin of the universe. Ansai Yamazaki pointed out that myths published in “Kojiki” and “Nihonshoki” in Japan presented the origin of the world. Beyond Yi Toegye, Ansai Yamazaki claimed that he was the ‘first person after Chu Hsi and said that Shintoism and Japanese history could be interpreted through Neo Confucianism. He also founded Suika Shinto. His idea deviated from Neo Confucianism by expressing, “If Confucius and Mencius attack Japan, we should take them all prisoner.” Neo-Confucianism after being introduced to Japan, was Japaneseized to a large because it was difficult to escape the influence of Buddhism or Shintoism.　In other words, Japanese Neo-Confucianism has turned into a Japanese-style camp logic.