This research is an attempt to study and evaluate the maintenance function at Factory 7 - The State General Company for Leather Industries, and to design a computerized preventive maintenance system to design and to analyze preventive  maintenance.  To accomplish the objectives of this research, data were gathered and analyzed according to the reliability engineering criteria for the period 2/1– 30/6/2005, then a preventive maintenance plan was designed for each machine of the sample study using the computerized system designed in this research. A Monte Carlo Simulation methodology was used for the purpose of evaluating the performance of the preventive maintenance plan of each machine for one year. The simulation results were used in performing significance tests of the research hypothesis. The significance tests revealed that the performance criteria of the preventive maintenance plans designed here were significantly different than the actual performance criteria. This research recommends the use of the computerized system and the preventive maintenance plans derived in this research.