We have conducted a first-principles room-temperature molecular dynamics (MD) simulations of gmelinite. For one water molecule, the MD provides a complete scenario of the reaction pathway of the spontaneous proton transfer (PT). Water adsorbs at the acid site (i). One hydrogen atom of the adsorbed water connects to the framework O atom (ii) constituting a six-membered ring. Within this ring, the water molecule attracts the acidic proton, thus creating an unstable hydronium cation (H3O+) (iii). Another proton then transfers to the framework and completes the intrazeolite PT (iv). The calculated adsorption energy of one water molecule is 107 kJ/mol.