Disclosed is a method for efficiently and highly selectively producing L-2-amino-4-(hydroxymethylphosphinyl)-butanoic acid, which is useful as a herbicide, through a catalytic asymmetric synthesis reaction. Specifically disclosed is a method for producing L-2-amino-4-(hydroxymethylphosphinyl)-butanoic acid which is characterized in that a dehydroamino acid is subjected to an asymmetric hydrogenation by using a rhodium catalyst represented by the formula (2) below and having an optically active cyclic phosphine ligand, and then the resulting product is subjected to hydrolysis: [Rh(R4)(L)]X   (2) [where R4 represents 1,5-cyclooctadien or norbornadien; L represents a substance represented by the following formula (6): (wherein R5 and R8 respectively represent a C1-4 alkyl group; R6 and R7 respectively represent hydrogen atom or hydroxyl group; and Y represents a group selected from groups represented by the following formula (7): (where Me represents methyl group)).].