Our project is based on the "Implementation of a Data Mart database for the granting of bank loans at the Caisse d'Epargne Congolaise, (CADECO in acronym)", the objective pursued in this project is the implementation of a decision-making system application to meet the needs of the latter. Our contribution to the study was to produce a Data Mart on the granting of loans, and from this we built a decision tree which we interpreted at the end, and finally this tool enables the decision-maker to have a central vision of all the staff, enabling him to take a strategic decision. This new system we have just set up consists of automatic management of customers, with the said system, we hope that the management of decision-making at CADECO will become easy and pleasant, since it will enable certain difficulties to be resolved.