Abstract: Cultural heritage has been damaged to varying degrees by long-term natural erosion and human activities. Traditional restoration materials have obvious defects, making them difficult to adapt to the fragile structure of cultural relics, and most restoration processes are irreversible. Developing green and efficient new restoration materials has gradually become a key demand in the field of cultural heritage restoration. As a natural macromolecular material, nanocellulose has been widely used in cultural heritage restoration due to its significant biocompatibility, high optical transparency, excellent mechanical strength, and large specific surface area with abundant hydroxyl groups. The application progress of nanocellulose and its composites in cultural heritage restoration was reviewed. The structural characteristics and properties of plant-derived nanocelluloses (including cellulose nanocrystals, CNCs; cellulose nanofibrils, CNFs) and bio-based nanocellulose (BNC) were systematically analyzed. The practices of their application in the restoration of paper, textiles, ancient wood, and paintings via brushing, spraying, dipping, and other application methods were discussed. The results showed that nanocellulose and its composites, with the advantages of good biocompatibility, environmental friendliness, and tunable functions, have effectively solved the problems of poor compatibility and easy secondary damage caused by traditional restoration materials. They provide an environmentally friendly and feasible new solution for cultural heritage restoration.