Handing over safe deposit boxes in the form of a lease contract is one of the types of banking services provided by banks to their customers. The discussion about the legal nature of this service is one of the challenging topics in banking law; However, until now, a comprehensive law that can explain its nature and elements has not been approved in this field. This has turned into a dispute between lawyers and experts in the banking system regarding the legal nature of the relationship between the bank and the customer. Because, on the one hand, the nature of this relationship is similar to the rules of the deposit contract and on the other hand, to the rules of the rental contract. The existing disagreements about the nature of trust fund rental contracts motivated the researcher to explain the existing rules in a descriptive way and using content analysis and finally come to the conclusion that the legal relationship between the bank and the customer regarding trust funds Trusts cannot be applied to deposit and rental contracts, and it is better to look at and interpret them as a special contract under the title of "protection contract" and within the framework of Article 10 of the Civil Law, with a special and independent nature with its own special conditions and provisions.