The closed cooling system is one of the systems that functioned to ensure the cooling water supply can be continuously distributed and ensure that the production process does not cause the equipment or products to overheat, which can result in failure to the equipment and affect the production process due to downtime repair. Reliability Centered Maintenance (RCM) is one of the methods that can be used to analyze the cause of failure, impact, and determination of appropriate and effective maintenance tasks. The purpose of this research is to identify potential failures, determine the maintenance task and determine the optimal maintenance schedule in the closed cooling system of a steam power plant by using the Reliability Centered Maintenance method. The results of analysis on the closed cooling pump, heat exchanger, expansion tank, minimum flow valve, and level control valve obtained a total of 155 failure modes, of which 73% of total failure modes were identified as an evident failure and 27% identified as a hidden failure. While the results of the maintenance task recommendation obtained a total of 155 maintenance tasks which consists of 5 maintenance task categories. They are 88 (57%) of total failure modes recommended to scheduled on condition task, 38 (24%) scheduled restoration task, 20 (13%) scheduled discard task, 3 (2%) schedule finding failure, and 6 (4%) of total failure modes recommended to no scheduled maintenance.