Due to the significant role that machining parameters play in performing successful and efficient machining operations, determination of the best or optimum machining parameters is still the subject of many studies. The need to use optimum machining parameters to improve machining economy is of greater importance when NC machines with high capital cost are employed. This paper describes development and utilization of an optimization system which determines optimum machining parameters for milling operations. Optimum machining parameters are intended for use by NC milling machines. However, they can also be used by conventional milling machines. A case has been studied at the end of the paper.