It is an object of the present invention to provide a method for producing a hair cosmetic product comprising protein nanoparticles which is obtained by mixing an aqueous medium and an oil medium, wherein the method enables stable emulsification without losing the performance of the protein nanoparticles. The present invention provides a method for producing a hair cosmetic product containing protein nanoparticles which is obtained by mixing an aqueous medium and an oil medium, wherein (a) protein nanoparticles having a mean particle size of 10 to 200 nm are mixed with an aqueous medium having a pH value different from the isoelectric point of the protein at an amount of 0.01% by weight to 5% by weight based on the total weight of the entire solution and (b) the obtained liquid is mixed with a substance selected from a cationic substance and an anionic substance, which has an electric charge that is on the same side as that of the protein obtained in the step (a) .
