The method of the production of a nanoparticle of the present invention includes a step of forming a nanoparticle of a group II group VI compound semiconductor in the cavity part of a protein, in a solution containing the protein having a cavity part therein represented by apoferritin, the group II element ion represented by Cd and Zn, and the group VI element ion represented by S and Se. Preferably, the solution further includes an ammonium ion, and the supply of the group VI element ion (X.sup.2-) into the solution is conducted by adding H.sub.2NCXNH.sub.2 to the solution. According to the aforementioned method, semiconductor nanoparticles having a uniform particle size can be produced.