In this study, we consider preventive maintenance planning for a component subject to failure. While earlier studies in literature consider the problem using failure rate, reliability is used in this study. Whenever the component's reliability falls below the reliability threshold R, an imperfect preventive maintenance is performed, which causes more frequent preventive maintenance over time. We use a hybrid reliability approach for modeling the effect of imperfect maintenance. We model total expected cost over all cycles, which can be used in making the optimal preventive maintenance plan. © Izmir University of Economics, Turkey, 2010.