The reaction H2NCH2CN + H2O→H2NCH2C(OH)NH is an important reaction related to the formation of glycine in the interstellar medium (ISM) and the origin of amino acids in early Earth. This reaction in the gas phase proceeds slowly and this is confirmed by its energy barrier of 254.7 kJ·mol-1 as determined at the MP2/6-311+(d,p) level without considering hydrogen tunneling in the ISM. On icy grain surfaces in the ISM, however, its reactivity may be enhanced by H2Ocatalytic reactions. The reaction of H2NCH2CNwith (H2O)3 is optimal as two H2Omolecules act as a catalyst with reducing the activation energy by 77.5 kJ·mol-1 and the activation free energy by 70.9 kJ·mol-1. A proton moves in a concerted way through a hydrogen bonded bridge. Quantum hydrogen tunneling is a crucial pathway for this reaction to proceed and was investigated using the small curvature tunneling (SCT) approximation and canonical variational transition state theory (CVT). At 50 K, rate constant kSCT/CVT is 1.86×10-23 cm3·molecule-1·s-1, which demonstrates that the reaction is feasible by a hydrogen tunneling mechanism in the ISM. These results may support the theory that the origin of amino acids is fromthe materials of the Earth itself.