The objective of our research is to audit the supply function, particularly the process of purchasing, inventory and fuel management. This is why we considered necessary to treat in the first part the stakes of an effective internal control within the supply function where we will try to recall the importance of the supply function in the company, its sub-processes, the associated risks and the necessity to control them. In the second part, we will try to describe our internal audit methodology by illustrating and identifying the aspects likely to be at the origin of possible dysfunctions; then we will propose some solutions to remedy the facts observed with an aim of optimization.