The present invention provides a method of producing an aqueous solution containing bis(N µ -lauroyl lysine)dicarboxylic acid diamide and/or a salt thereof, and having a pH of 9 - 11, which includes a first step of reacting N µ -lauroyl lysine and/or a salt thereof with dicarboxylic acid dichloride in a water solvent having a pH of 12 - 14 to form bis(N µ -lauroyl lysine)dicarboxylic acid diamide and/or a salt thereof, a second step of adjusting the aqueous solution obtained in the first step to pH 7.5 - 8.5, a third step of adding N µ -lauroyl lysine to the aqueous solution obtained in the second step and filtering the mixture, and a fourth step of adjusting the aqueous solution obtained in the third step to pH 9 - 11.
