International Baccalaureate (called IB) has expanded its number in various parts of the world. This paper shows how IB programmes spanning the world change educational practices in the particular region and country, with a focus on Japan. There are a number of educational elements peculiar to Japan (the homeroom system, the comprehensive role of teachers, club activities, etc.) that present barriers to the introduction of Western-oriented IB programmes. At the same time, the government intends to improve its quality by incorporating IB into existing education curriculum in Japan. Though comparing Japan's public/private IB (and non IB) schools with International schools that offer IB programmes, this paper has significance in the aspect of investigating how the problems peculiar to that country are occurring in the practice of IB in Japan, non-Western country, and of leading to an understanding of how changing educational practices can create merits and difficulties when attempting to merge national educational practices with overseas educational elements.