Although ZrB12 is a promising advanced material because of the boron cuboctahedron cages, the hardness of ZrB12 remains controversy. Here, we apply first‐principles calculations to study the influence of transition metals (4d‐ and 5d‐) on the hardness and thermodynamic properties of ZrB12. The calculated hardness of ZrB12 is 32.9 GPa, which is in good agreement with the previous theoretical result. Importantly, the calculated hardness of Re‐doped ZrB12 is up to 40.0 GPa, which is a potential superhard material. The essential reason is that the alloying element of Re enhances the localized hybridization of BB and ZrB atoms, and then forms the strong BB covalent bond and ZrB bond. The result is well demonstrated by the chemical bonding and lattice parameter. Here, our work shows that the alloying elements of Nb, Mo, and Re enhance the thermodynamic properties of ZrB12. The Debye temperature of Re‐doped ZrB12 is 1225.2 K, which is larger than that of the parent ZrB12 (1213.5 K).