Japan has made remarkable progress in water supply and sanitation during the past 100 years. On the other hand, many developing countries lack adequate water supply and sanitation facilities, which causes high mortality rates. The 'International Drinking Water Supply and Sanitation Decade' (IDWSSD) has been promulgated by the UN since 1981 to cope with this problem. Japan has made efforts to develop foreign assistance projects in the water supply and sanitation field since 1968. Recently, after the promulgation of IDWSSD, such activities have been expanded. However, there exist many problems in Japanese economic and technical assistance partly because Japan has rather less experience in foreign assistance than other advanced countries. Therefore effective measures should be taken to conduct more appropriate foreign aid programs.