Islamic bank is a bank which is operating in accordance wwith islamic sharia principles. In realizing Mudharabah Akad in terms of Islamic Shari’ah (islamic law) and overcome the risk of loss in Islamic Banking would need to be studied and understood. Islamic Bank forbids interest. Therefore, it does not use the interest mechanism in its operations, so the institution which guarantees the customer deposits does not use the mechanism of interest. Operationally using the contract that has been determined in islamic jurisprudence, the institution that guarantees the customer deposits should be based on the contract that is specified in islamic jurisprudence. The type of this research is normative legal research (legal research). It uses library study method and interview with the informant. All the data will be processed by using perspective method. This research aims to understand the principle of mudharabah contract in saving deposit by using credibilty system between shahibul maal ( customer) and mudharib ( fund manager). In credibility system, customer will hand over the fund to the bank. the problem of financial loss occurs when the bank spread the customer’s money and entrust to the third party. If there is a financial loss, shaibul maal and mudharib should bear the problem. From the weakness, there is no removal of the mudharabah contract. Based on the practice, there is always an openness between bank (mudharib) and customer (shahibul maal).