The article presents the steps of modeling of the material management system in a manufacturing company. First, the modeling procedures indicating by Forrester, Łukaszewicz, Souček, Tarajkowski and Sterman were described and the essence of materials management in a manufacturing company was presented. Next, modeling of the materials management system was shown - step by step. Initially, the variables of the mental model connected with materials were defined, then variables in casual loop diagrams were linked. Diagrams were transformed into a simulation model that has been verified. The validation of the simulation model was conducted by using the following methods: assessing the correctness of the boundary of modeling, adequacy of the model structure and adopted values (constants) compared with available knowledge about the modelled system; test of the accuracy and consistency of the units of variables adopted in the model and test of the model behavior in extreme conditions. The study endpoints included the simulation of the model on empirical data, which were collected in the company Alpha and test of the “what ... if ...”. The test showed that the small changes in control norms (constants), which control the system, could have influenced to more rational management of that system.