Abstract: This study describes the development of a decision support system to assist in the master production planning for a Just-In-Time mass production system. The prototype system determines the optimum production rate to be produced for each intended product while considering demand requirements, capacity limitations and lot sizing. A unifying model, based on goal programming, was employed to solve the production planning issues involved in reaching the optimal Master Production Schedule (MPS). The developed prototype decision support system interfaces with Lingo 7.0 via Visual Basic in a Microsoft Windows environment. It provides the decision maker with a friendly tool for planning production under various circumstances. The system was successfully validated through literature test cases by comparing its results against those yielded by the existing optimization algorithms.