AbstractThe hydrogen abstraction reactions from hydrazine and its methyl derivatives by the H atom have been investigated theoretically by using CBS‐QB3//DSD‐BLYP‐D3(BJ)/Def2‐TZVP quantum chemical calculations and transition state theory calculations coupled with various tunneling correction methods. Both the products and transition state energies of the hydrogen abstraction from the amino group were stabilized by the methyl group substitution. The substitution effect on the αN site was two times larger than that on the βN site. On the other hand, the substitution effect was negligible on the hydrogen abstraction from the methyl group. The overall rate coefficients of N2H4 + H reaction calculated by canonical variational transition state theory with the small‐curvature tunneling correction agreed well with previously reported values, but those of CH3NHNH2/(CH3)2NNH2 + H were slightly lower than a previous experimental value. The product‐specific rate coefficients have been proposed for the kinetics modeling of these fuels’ combustion.