PURPOSE: To obtain the titled compound useful as a synthetic raw material for peptides, in high yield with small amounts of a by-product and thionyl chloride to be used, by reacting an amino acid with the thionyl chloride in a solvent in the presence of a tertiary amine.

CONSTITUTION: An amino acid is reacted with thinyl chloride in a slovent in the presence of a tertiary amine, e.g. triethylamine or pyridine, at 0W30°C, preferably 20W25°C, to give the aimed amino acid chloride. The amount of the thionyl chloride to be used is 3 equivalents or less, preferably 1W2 equivalents, based on the amino acid, and the amount of the tertiary amine to be used is equivalent or more, preferably about 1.3W2.6 equivalents, based on the amino acid. A halogenated hydrocarbon, e.g. methylene chloride or chloroform, may be preferred for the solvent used in the reaction. Glycine, alanine, etc. may be cited as the raw material amino acid, and the amino group is usually protected for use.