Tujuan Penelitian: Menganalisis efektivitas sistem pengendalian internal persediaan di PT Megamas Plaza Bangunan dengan kerangka COSO.Metode: Pendekatan deskriptif kualitatif melalui wawancara dengan pihak terkait dan analisis dokumen perusahaan.Originalitas/Kebaharuan: Penelitian memberikan evaluasi komprehensif praktik pengendalian persediaan di ritel bahan bangunan Indonesia menggunakan komponen COSO.Hasil: Implementasi pengendalian internal secara umum baik, terutama pada lingkungan pengendalian dan sistem informasi, namun ditemukan kelemahan dalam pemisahan tugas dan frekuensi pemantauan.Implikasi: Disarankan adopsi teknologi otomatisasi real-time, penjelasan pembagian tanggung jawab, peningkatan frekuensi stok opname, dan pelatihan karyawan untuk optimalisasi pengendalian internal. Research Objective: This study analyzes the effectiveness of the internal control system for inventory management at PT Megamas Plaza Bangunan using the COSO framework.Methodology: A qualitative descriptive approach was employed through interviews with key personnel and analysis of company documents.Originality/Novelty: The research provides a comprehensive evaluation of inventory control practices in Indonesia's building materials retail sector using COSO components.Findings: Results indicate generally good implementation of internal controls, particularly in control environment and information systems, though weaknesses were found in task segregation and monitoring frequency.Implications: The study recommends adopting real-time inventory automation technology, clarifying division of responsibilities, increasing stock-taking frequency, and enhancing employee training to optimize internal controls.