PURPOSE: To mass produce the titled compound to be expected as an optically resolving agent at low material cost, by optically resolving N-acetyl-DL-glutamic acid with a compound derived from de-carnitine nitrile chloride.

CONSTITUTION: d-Carnitine nitrile chloride is converted into d-carnitine nitrile hydroxide, N-acetyl-DL-glutamic acid is optically resolved with d-carnitine nitrile hydroxide and N-acetyl-L-glutamic acid recovered after optical resolution is recemized with water under pressure by heating at ≥150°C to give DL- pyroglutamic acid. Then this compound is heated with an alkali aqueous solution, without isolation, and an acetylating agent is dripped to the aqueous solution to give N-acetyl-DL-glutamic acid. In the operation, characteristically the product after the optical resolution is subjected to acidolysis with conc. hydrochloric acid.