This study aims to synthesize a new BSA-MXene/Au-PDTC nanocomposite and evaluate its free-radical scavenging ability and antioxidant potential. The BSA coating can greatly improve the dispersibility and stability of MXene and allows the Au-PDTC complexes to be evenly loaded on its surface, forming an antioxidant composite material. In the DPPH, ABTS, and Folin–Ciocalteu assays, the material showed strong free-radical scavenging and reducing abilities, and it also effectively reduced ROS generation in the DCFH-DA cell model. Scanning electron microscope showed that BSA prevents the restacking of MXene layers, while Au-PDTC appeared as nanoparticle dots evenly distributed on the MXene surface, confirming the surface functionalization of the composite. The PrestoBlue cell-viability assay also showed that the composite had much lower cytotoxicity than Au-PDTC, which matches reports saying that protein coating can reduce the cytotoxicity of gold ions. Owing to its good antioxidant ability and biocompatibility, the BSA-MXene/Au-PDTC nanocomposite shows potential as an antioxidant material in biomedical applications.