This paper presents results about the optimal order interval in a context of fuzzy information about inventory management. The classical inventory model is based on well known cost and demand rate. In practice, this accurate estimation is very difficult to obtain, even impossible. Consequently, we propose a solution, not optimal in a classical sense, but allowing to choose an action which is not far from the optimal policy whatever the economic parameters may be. These parameters belong to a field which represents the error of estimation, this field is important to choose the solution.