This study investigates the influence of tannic acid (TA), a natural plant-based biomolecule, on the hydration of tricalcium aluminate (C3A)-gypsum systems, aiming to elucidate its potential as a novel concrete strength enhancer. To this end, detailed investigations were conducted into the hydration and nano-mechanical properties of C3A-gypsum system regarding the content of sulfate. In the absence of gypsum, the addition of TA accelerates the hydration of C3A, leading to a 30.6 % increase in accumulated heat until 10 h. This acceleration is attributed to TA's intercalation with metastable hydration products, impeding their transformation into final hydrates (C3AH6). Characterization using XRD, TGA, and FTIR techniques confirms the presence of hexagonal hydrates as the main hydration products in C3A-TA pastes, while the main hydration products in C3A-DI pastes was cubic one. In scenarios involving gypsum, TA markedly retards the hydration of C3A-gypsum mixtures, with SEM analysis indicating the promotion of AFt formation at low sulfate content while inhibiting its transformation to AFm. Furthermore, comprehensive nanoindentation results demonstrate that TA consistently enhances the micromechanical properties of C3A-gypsum hydrates, irrespective of gypsum content. This study provides valuable insights into the mechanisms through which TA influences the hydration of C3A-gypsum systems, offering promising avenues for enhancing the performance of concrete materials.