The adequate management program of spare parts (Maintenance Repair and Overhaul / MRO Material) is crucial for industries to strike a balance between maintaining optimum stock levels and ensuring uninterrupted plant availability. In this paper, we propose an approach that utilizes stock holding policy (SHP) to optimize spare part stock, reducing costs while guaranteeing availability critical components towards Subsidiaries companies under Indonesian Fertilizer Holding Companies (IFHC) which never been implemented effectively before. Several studies have addressed the challenge of stock optimization for spare parts, considering factors like demand variability, lead times, and the impact on plant availability. However, most approaches tend to focus solely on cost reduction, often overlooking the implications on plant maintenance and overall productivity. When stock out occurred. Our proposed SHP methodology based on specifically integration of maintenance strategy, stock out effect, and demand anticipation, and the output was integrated with inventory strategy into the spare parts management process. By leveraging historical usage data and predictive analytics, we aim to strike a balance that minimizes inventory carrying costs while safeguarding against stockouts that could lead to extended plant downtimes. To ensure the accuracy and reliability of our optimization model, extensive data on spare part usage, lead times, maintenance strategy, stock out effect and Failure Mode were collected and analyzed. This data-driven approach allows us to tailor the SHP to the specific needs of the plant. The results demonstrate that by implementing the proposed SHP, the overall stock of spare parts can be significantly reduced without compromising plant availability. The optimized stock holding showed a substantial decrease in existing inventory value exploited from MRP type change from stock to non-stock (approximately 30% from total material value analyzed, 9 million USD), leading to enhanced cost- efficiency for the organization. The plant's spare parts inventory was optimized through SHP, resulting in a 30% reduction in MRO Material Value, while 70% of the MRO Material which has been analyzed, categorized as stock material and identify to prevent potential loss of 110 million USD In conclusion, the utilization of SHP aligning IFHC's objective with practical and effective means to optimize spare part stock, ensuring the right balance between cost-saving measures and maintaining plant availability. By employing data-driven decision-making processes, industries can achieve long-term sustainability, improved performance, and reduced operational risks.