Provided is a method for producing a nanoparticle having a uniform particle diameter. A method for producing a nanoparticle comprising an amphiphilic block polymer, the method comprising: with use of a nanoparticle production device that includes: a polymer solution supply channel Cp an aqueous liquid supply channel Cw1, Cw2 a junction J of the channels a nanoparticle formation channel Cn and a nanoparticle-containing liquid outlet On, supplying a solution of a polymer and an aqueous liquid to the junction J forming a nanoparticle while bringing a laminar flow of the polymer solution and a laminar flow of the aqueous liquid into contact with each other obtaining a liquid containing the formed nanoparticle from the nanoparticle-containing liquid outlet and controlling a particle diameter of the nanoparticle by measuring a statistic of the particle diameter of the formed nanoparticle in real time, and by controlling at least one of an amount of the polymer solution supplied to the junction and an amount of the aqueous liquid supplied to the junction such that the statistic becomes a desired value.
