An object of the present invention is to obtain a zinc oxide-protein complex which can be a source of nanoparticles of zinc oxide utilizing a protein having a cavity inside thereof. The process for producing a zinc oxide-protein complex according to the present invention includes a hydrogen peroxide addition step for adding hydrogen peroxide so that the concentration would be 60 mM or greater and 150 mM or less to a buffer containing a protein having a cavity inside thereof such as ferritin, zinc ion, and ammonia.