Metal nanoparticle composite body, metal colloidal solution, and method for producing metal colloidal solution

Provided are: a metal nanoparticle composite body which is capable of achieving more practical conductivity by intentionally adding/adjusting a plurality of properties, namely good metal nanoparticle controlling ability, high dispersion stability, good low-temperature firing properties, and easy separability of metal nanoparticles through purification; a metal colloidal solution which is obtained by dispersing the metal nanoparticle composite body; and a method for producing the metal colloidal solution. A metal nanoparticle composite body containing a nitrogen-containing compound (A) and metal nanoparticles (B), which is characterized in that the nitrogen-containing compound (A) contains an oxidized nitrogen atom; a metal colloidal solution which is characterized by being obtained by dispersing the metal nanoparticle composite body in a medium; and a method for producing a metal colloidal solution, which is characterized in that metal nanoparticles (B) are obtained by reducing metal ions in a medium in the p