PURPOSE: To produce an N-alkoxycarbonylamino acid through a simple operation.

CONSTITUTION: A dialkyl dicarbonate, for example, di-t-butyl dicarbonate and an amino acid, for example, L-proline are allowed to react with each other in an organic solvent compatible with water such as t-butanol to form an N- alkoxycarbonylamino acid, for example, N-t-butoxycarbonyl-L-proline, which is then mixed with water to give the N-alkoxycarbonylamino acid including a reduced amount of unreacting starting substance.