A commercial polyvinylpyridine polymer has been used for the in situ preparation of magnetic nanocomposites. Several procedures have been followed in the preparation of the nanoparticles based on the formation of polymer-metal complex gels. The use of mixtures of protic and aprotic solvents for the reaction of the polymer with the metal salts is discussed. Superparamagnetic nanoparticles of CoO and Fe2O3 have been obtained with an average size of 50 and 10 nm, respectively. The utility of nitrogen base polymers for the fabrication of magnetic nanocomposites is emphasized.