With the rapid expansion of global aquaculture, the annual production of discarded oyster shells has surged, but their improper disposal through landfilling or indiscriminate dumping can lead to severe environmental pollution and resource waste. Oyster shells, comprising 90%~95% calcium carbonate (CaCO3), organic matrices, and trace elements (e.g., zinc and selenium), exhibit multifaceted bioactivities including antimicrobial, antioxidant, and immunomodulatory properties. However, their highvalue utilization remains constrained by technical limitations in processing methodologies. This review systematically analyzes the chemical composition, processing techniques, nutritional components, and bioactivity profiles of oyster shells and summarizes their emerging applications in food preservation, nutraceutical formulations, cosmetic ingredients, and biomedical materials. Critical bottlenecks in industrial applications, such as inefficient bioactivity retention, heavy metal residues, and high energy consumption during nanonization, are discussed. To address these challenges, future developments should prioritize artificial intelligencedriven green processing optimization and microbial-enzyme synergistic heavy-metal detoxification. Gaining precise control over the processes of nanonization and bioactivity retention will enable the transformation of oyster shells into high-value products, such as pH-responsive drug carriers, biomimetic bone repair scaffolds, and high-bioavailability calcium fortifiers. By establishing a comprehensive industrial chain from aquaculture waste to multifunctional materials, synergistic improvements in ecological and economic benefits can be achieved.