The method of the production of a nanoparticle of the present invention includes a step of forming a nanoparticle including a compound of ametal ion in a cavity part of aprotein, in a solution containing the protein having the cavity part therein, the metal ion, and a carbonate ion and/or a hydrogen carbonate ion. Examples of the aforementioned compound include e.g., a hydroxide. The aforementioned metal ion is preferably any one of a nickel ion (Ni.sup.2+), a chromium ion (Cr.sup.2+) or a copper ion (Cu.sup.2+). According to the aforementioned method, nanoparticles having a uniform particle diameter can be produced.