Prudent banking principle is one of the most important principle in Indonesia banking system. The principles represent important factor to make a healthy and strong banking system. This principle is written at the banking act No 10 year 1998 jo No 7 year 1992 that by doing all banking services use prudent banking principles base on economic democracy. Although it is written, it does not have the exact meaning. Therefore the implementation of this principle becomes miss-interpreted and by majority understanding it is strongly interpreted only for bank to use and run the banking activities with it. Nowadays, banking costumers become less careful and also assume that just only bank that have to be noticed. The principles made to force not only bank or regulator such as central bank and Financial Services Authority (OJK), but also costumer of the bank itself. There is an issue that come with case No: 769K/Pdt.Sus/2011 that told us the importance of prudent banking principle not only for bank to ran but also for bank’s customer itself. Customer in this case not doing his duty to keep his personal identification numbers (PIN) for anyone without exception. In fact he gives the bank card to his wife that is not right and his wife got accident from several people in the ATM machine that took the money from his husband account. Both bank and customer had a contract before they committed as party and it is mean they got rights and obligations to be done. As a unity in the banking system, all members have to use and run the prudent banking principles as well as possible. By this thesis, I would like to elaborate the meaning of prudent banking principles become more obvious