This research aims to analyze the substance of related jurisprudence underlying asset in islamic economic law, analyzing the position of the system underlying asset in the financing agreement musharakah mutanaqisah (mmq) in the perspective of islamic economic law, and analyzing the application of the system underlying assets in the agreement musharakah mutanaqisah on sharia banking. This type of research is an empirical research type. Data is qualified as primary data and secondary data. Primary data was obtained through interviews and secondary data was obtained through literature study. The data collected was then processed using a qualitative analysis approach. The research results show that: 1) Underlying Asset position is based on the substance of fiqh as the basis for cooperation in an MMq contract, 2) Position Underlying Asset in the Musyarakah Mutanaqisah Agreement it can be categorized as the basis for cooperation in an MMq contract. In Islamic economic law, regarding the issue of musyarakah objects or MMQ objects being used as collateral, Islam prohibits goods used as transaction objects from becoming collateral/guarantee for the implementation of a mutual agreement, when the rental object has not beentangible when the contract is made, 3) The application of collateral in sharia banking is absolutely unavoidable. Requests for guarantees by banks from recipients of financing facilities are not only intended to ensure the return of the capital borrowed, but to ensure that recipients of financing facilities actually carry out everything that has been agreed upon in the contract, including Underlying Assets as a basis in the issuance of MMq contracts.