Penelitian ini bertujuan untuk menganalisis struktur biaya penanganan keluhan pelanggan serta pengaruhnya terhadap margin keuntungan pada Cahaya Department Store. Metode penelitian yang digunakan adalah kualitatif deskriptif dengan triangulasi data melalui wawancara mendalam, observasi partisipatif, dan analisis dokumen. Hasil penelitian menunjukkan adanya lima komponen biaya utama, yaitu tenaga kerja (65%), teknologi informasi (18%), kompensasi langsung (12%), operasional (3%), dan pelatihan (2%). Ditemukan adanya inefisiensi dalam alokasi biaya, ditunjukkan oleh 40% keluhan yang bersifat berulang serta disparitas biaya antara keluhan product defect dan service quality. Meskipun terdapat korelasi negatif jangka pendek antara biaya penanganan keluhan dan margin keuntungan, investasi jangka panjang menunjukkan peningkatan customer lifetime value hingga 2,3 kali lipat. Penelitian ini menegaskan pentingnya optimalisasi biaya penanganan keluhan melalui penerapan predictive analytics, self-service portal, dynamic pricing, dan continuous improvement sebagai strategi untuk meningkatkan efisiensi, profitabilitas, serta loyalitas pelanggan pada industri ritel modern. This study aims to analyze the cost structure of customer complaint handling and its impact on profit margins at Cahaya Department Store. The research employs a descriptive qualitative method with data triangulation through in-depth interviews, participatory observation, and document analysis. The findings reveal five main cost components: labor (65%), information technology (18%), direct compensation (12%), operations (3%), and training (2%). Inefficiencies were identified, with 40% of complaints being repetitive and cost disparities between product defect and service quality cases. Although a short-term negative correlation exists between complaint-handling costs and profit margins, long-term investment analysis shows an increase in customer lifetime value by up to 2.3 times. This research emphasizes the importance of cost optimization through predictive analytics, self-service portals, dynamic pricing, and continuous improvement strategies to enhance efficiency, profitability, and customer loyalty in the modern retail sector.