Abstract：As a renewable source of energy, ethanol has been widely used in internal combustion engines as either gasoline alternative fuel or fuel additive. However, as the chemical source term of computational fluid dynamics (CFD) simulation of combustors, it remains disagreement on understanding of chemical kinetic mechanism of ethanol. Reaction mechanism of ethanol + H?2 is well known a crucial reaction class in terms of predicting reactivity of ethanol as well as ethylene formation at engine relevant condition. However, the kinetic parameters of the reactions are basically extrapolated by analogy with n-butanol + H?2 system calculated by Zhou et al. (Zhou et al. International Journal of Chemical Kinetics, 2012, 44 (3), 155-164). The reliability of such the analogy remains to be seen, as no directly theoretical or experimental evidence is available in literature to date. In this study, thermal rate coefficients of H-atom abstraction reactions for ethanol + H?2 system were determined by using both conventional transition-state theory and canonical variational transition-state theory, with the potential energy surface evaluated at the CCSD(T)/cc-pVTZ//M06-2x/def-TZVP level. The quantum mechanical effects were corrected by zero-curvature tunneling method at low temperatures (< 750 K), and difference schemes of two Eckart functions were fitted to optimize the minimum energy path curves. Torsional modes of the -CH3 and -OH groups were treated by using the hindered-internal-rotator approximation. Furthermore, the rate coefficients of the title reaction were calculated at both CCSD(T)/cc-pVTZ//M06-2x/def-TZVP and CCSD(T)/CBS//M06-2x/def-TZVP levels of theory with an uncertainty of a factor of 3. Similar to n-butanol + H?2 system, the title system is dominated by alpha site H-atom abstraction, but the rate coefficients of the three channels are slightly slower than that of n-butanol + H?2 system. Generally, the new calculations show only limited effect on ethanol reactivity at low pressures and high temperatures (over 1300 K) but it prevents the kinetic mechanisms to over-predict ignition delay times under engine relevant conditions.