Ocean Thermal Energy Conversion (OTEC) is a foundation for an appealing renewable energy technology with regards to its vast and inexhaustible resources of energy, renewability, stability, and sustainable output. The principle of an OTEC power plant is to exploit the energy stored in between the upper layer of warm surface seawater (heat source), and the cold layer of deep seawater (heat sink). The plant operates based on a Rankine cycle to produce electricity between the source and the sink at the minimum temperature difference of approximately 20 K. The main objective of this study is to evaluate the performance of the proposed OTEC closed Rankine cycle using ammonia as the working fluid, to be paralleled with basic OTEC Rankine cycle. Preliminary simulation was performed at the initial stage of the study to validate the simulation model by referring to previous OTEC studies. The same developed model was deployed to test the efficiency of the proposed modified OTEC Rankine cycle, resulting in an enhancement in terms of thermal cycle performance from 3.43% to 7.98%. This study has revealed that the proposed OTEC closed Rankine cycle which introduced an interstage superheating as well as an improved condenser cooling system, augmented the system competence of an OTEC power cycle.