To provide a process for producing nanoparticles having a controlled target particle diameter, in the process for bringing a pigment solution into contact with a poor solvent in a reactor having channels to precipitate pigment nanoparticles.

There is provided a process for producing pigment fine particles by using a reactor in which three or more tubular flow channels I and II and one or more discharge channels III disposed on one substantially identical surface are connected at one point, and allowing the pigment solution I prepared by dissolving a pigment in a good solvent and the solvent II compatible with the good solvent but being a poor solvent for the pigment to join in the connection point or the vicinity thereof to precipitate fine particles of the pigment, wherein the precipitation is performed by circulating both of the pigment solution and the poor solvent solution so as to be joined in a state where one of the solutions is intervened between the other, and regulating the degree of supersaturation of the pigment when the solutions are joined to control the average particle diameter of the resultant pigment fine particles.