Preventive maintenance is required for many important systems as failure occurrence results in great loss. Therefore, a sequential preventive maintenance decision procedure is proposed to maintain the hazard rate below the predefined level. A scheduled replacement with lower cost than failure replacement is required after several preventive maintenance actions. The time points (durations) for preventive maintenance and the scheduled replacement is determined by a proportional hazards model (PHM). The number of preventive maintenance is determined by the ratio of the average cost over the average lifetime. A Weibull lifetime system with known parameters is illustrated to carry out the proposed preventive maintenance decision procedure.