The present invention provides a method for producing asymmetrical mono-substituted alkylated compounds of α-amino acids that are represented by a specific formula, using an aldimine-type Schiff base. In the method of the present invention, the process of alkylating an aldimine-type Schiff base in a medium in the presence of an optically-active quaternary ammonium salt phase-transfer catalyst and an inorganic base is initiated, and subsequently the reaction is quenched at a time earlier than a time for completion of the stoichiometric reaction of the alkylation reaction, so that a mono-substituted alkylated product with high optical purity can be obtained.