P T. INTIRUB is a manuf.1cture company which produces tire v.i.th kinds of type. A problem usually occurs at this company is the high of breakdown frequency which one is caused by a lack of optimalization in maintenance management systems that had been implemented by this company. It could atTect the production process so the company difficult to reach the production target and cause decreasing quality of product. That's why the preventive maintenance is needed, especially for the critical machine, in order to decrease the downtime value and increase the availability together with it's reliability value.The ftrst stage involves tracking critical status machine based on the longest dov.ntime accumulated by the rnachines during perioo from April, 1st 2004 to Marc 3 1!'it 2005, then they are identified using Pareto chart, so that is gotten Tire Building as the critical machine. It's critical components are the components that had been breakdO\vn more than fourth during that period. Based on the downtime database, ifs gotten that the critical components are all components of Tire Building, which amonnts 13 components.Continued with conducting a scheme of maintenance procedure usiJ.1g RCM II approach, th..1t contains Functional Block Diagram, Root Cause Failure Analysis, and Failure Mode and Effect Analysis, then we have the order of components tlk'lt are suitable\\'ith the function to it's critical machine, analysis from it's frtilure factors, until we get a component which have the highest Risk Priority Number, it is Dnun component with the value of 1210.1ne nexi step is to choose the distributions from ftt to failure and repair data, and then will be tested again v.ith the special tests for every type of distribution'), do the calculation of parameter, Mean Time To Failure, and Mean Time To Repair using Maximum Likelihood Estimator method . To determine the optimal preventive replacement interval based on the minimizing downtime criteria. Optimal replacement interval, inspection time, availability , and order schedule for each parts can be provided. From the test comparisons between the present and snggested reliability, it can be concluded that reliability can be flk'lintained at a high standard by applying prevention maintenance which including preventive replacement and critical components in tions.The last step is calculating the reduce costs which overcome if they areapproximating between failure maintenance 's cost \\i.th preventive maintenance's C