Since the Organized Crime Group Prevention Act, which legally established organized crime groups as anti-social organizations, came into force in March 1992, earnest efforts have been made to block further transfer of funds to such groups and to prevent money laundering. However, last year, Mizuho Bank was found to have been lending money to anti-social organizations, which revealed that companies in Japan still do not have sufficient means to deal with such organizations appropriately. However, the closer look shows that this case is more complicated than what people understand through media and suggests there is high likelihood of Japanese big enterprises falling into tactful about dealing with anti-social organizations. This article aims to offer suggestions to improve the status quo by scrutinizing the Mizuho case in detail.