Abstract: A method of manufacturing a fine-particle colloid or a magnetic fluid of a metal nitride through reaction between a metal carbonyl and a nitride-bearing compound, a two-step reaction is performed, comprising a first-step reaction of synthesizing a nitrogen-bearing metal carbonyl which is a precursor substance and a second-step reaction of synthesizing metal nitride from said precursor substance. A step of eliminating unreacted metal carbonyl is provided between the two-step reaction. By repeatedly causing the series of reactions, a fine-particle colloid or a magnetic fluid of the metal nitride is manufactured. For the magnetic fluid, the solvent may be replaced in response to a particular purpose of use of application after production.