Master data management (MDM) of employee is used by the Information System of Personnel (SIKEP) and the Integrated Supreme Court Information System (SIMARI) in Supreme Court of Indonesia Republic (Supreme Court). SIKEP not yet used by all echelon I units in the Supreme Court. Therefore, it is necessary to identify problems where much data in SIKEP is not yet complete and valid. It is necessary to manage the master data of employees in the Supreme Court. The purpose of master data management assessment is to find out the extent of maturity of master data management (MDM) employee of Supreme Court Indonesia Republic (Supreme Court). This assessment is using management master data maturity model (MD3M) base on other research. The objective of this research paper is a practical nature. From a corporate point of view, the objective is to give organization to assess their employee MDM maturity. The result of assessment can identify potential improvement areas of Employee MDM. Final result of the maturity of the master data management of the Supreme Court is as follows; for business function data model and data quality maturity level is 1. The use and ownership and maturity level is 2. Business security function even reach the level of maturity 4. Therefore, the overall result of the maturity level of master data management in the Supreme Court is 1. This means that the Supreme Court already has awareness in the management of master data.