This study describes an efficient and solvent-free method for the regioselective production of L-lysine ammonium epsilon-carbamate by ball-milling L-lysine under an atmosphere of CO2. The regioselective formation of L-lysine ammonium epsilon-carbamate by this mechanochemical approach was confirmed by a complete analytical study, including 1H->13C and 1H->15N CP MAS NMR measurements as well as liquid NMR analysis, powder X-ray diffraction, thermal analysis, and elemental analysis. Time of milling, rotational speed, milling material, and liquid assistants were screened, while the reversibility of the process was assessed. This milling approach was compared with the syntheses in aqueous solution and in the solid-state without agitation. In addition to be regioselective, the synthesis by solvent-free mechanochemistry was found to be much faster than the other approaches while producing lot less waste.