Microtubules are cytoskeletal filaments characterized by dynamic instability at their tips and a dynamic lattice that undergoes continuous tubulin loss and incorporation. Tau, a neuronal microtubule-associated protein, is well known for its role in stabilizing microtubule tips and promoting microtubule bundling. Here we demonstrate that tau also modulates microtubule lattice dynamics. Although tau lacks enzymatic activity, it significantly accelerates tubulin exchange within the lattice, particularly at topological defect sites. Our findings indicate that tau enhances lattice anisotropy by stabilizing longitudinal tubulin–tubulin interactions while destabilizing lateral ones, thereby enhancing the mobility and annihilation of lattice defects. These results challenge the traditional view of tau as merely a passive stabilizer, revealing its active role in dynamically remodelling the microtubule lattice structure.