The kinetics of hydrogen abstraction reactions of monomethylhydrazine (MMH) by OH radical were investigated based on transition state theory with correction of quantum mechanical tunneling effects. The stationary points of the potential energy surfaces for the H-abstraction reactions were calculated at the CCSD(T)/6-311++G(d,p) level based on the geometries optimized by the BHandHLYP/6-311G(d,p) and MP2(full)/6-311G(d,p) methods. One MMH-OH preactivated complex and three MMH radical-H2O complexes were found on the potential energy surface with shallow wells. Intrinsic Reaction Coordinate (IRC) calculations were performed to confirm all transition states and their corresponding reactants and products. The total partition function of the target species was calculated with the framework of the rigid-rotor-harmonicoscillator approximation with the correction of internal rotations, and all the torsional motion on the single bonds between the heavy atoms were treated as hindered internal rotations. The calculated total rate coefficient on the H-abstractions of MMH + OH is in agreement with available experimental data.