Disclosed is a method for efficiently producing L-2-amino-4-(hydroxymethylphosphinyl)-butanoic acid, which is useful as a herbicide, by a catalytic asymmetric synthesis reaction with a high asymmetric yield. The production method comprises a step wherein a compound represented by the formula (1) below and a benzylamine are reacted in the presence of a dehydrating agent, then the resulting is reacted with hydrogen cyanide in the presence of an asymmetric catalyst, and then the resulting is subjected to acid hydrolysis which is followed by elimination of a protective group. [chemical formula 1](1) (In the formula, R<1> represents a C1-4 alkyl group).