Profit is a main objective of production units, and minimization of its maintenance cost will help to achieve it. But with no compromise with plant machinery reliability constraints. Manufacturing systems do require maintenance, but deferring it due to production constraints may increase its requirements, resulting in the increased cost. The experience shows that carrying out of the preventive maintenance (PM) helps in avoidance of catastrophic failures, but this needs to be optimized. An optimal PM interval will minimize maintenance cost, while maintaining their lower bound reliability. Most existing optimization models do not address this issue especially in the context of real life industries. Particle swarm optimization is an effective meta-heuristic technique and is extensively applied to find optimal solution for various engineering problems. In this paper, this is proposed for maintenance cost minimization of manufacturing systems under reliability constraint. An example is illustrated to demonstrate it.