since the economic crisis has begun, every organization search for solutions that allow firms to gain competitive advantage.

For this reason, almost of companies search to improve their management, one way for this is lean management.

In this paper we focus on the second muda of lean management, to produce for the customer the exact quantity needed. This result on eliminating excess stock or shortage wastes.

For the Moroccan firms who are self financing, they focused more on the search for new methodologies that allow them enhancing their financial results by decreasing costs and improving their process and customers satisfaction.

In this paper we choose to apply lean six-sigma for the calculation of inventory, using DMAIC. The proposed model is tested in a Moroccan spare parts company. Firstly, we have identified the inventory management problems and secondly we search of the root causes of these problems. In the third part we elaborate the action plan to resolve the problems and finally improve and control the results.