A process for producing a resorcinol-formalin resin containing no salts, having a moderate flowability when transformed into an aqueous solution, and having a reduced content of resorcinol monomer and a reduced content of resorcinol-formalin resin of resorcinol pentanuclear or higher nuclear bodies, the whole steps including an one-stage reaction and liquid-liquid distribution being conducted in the same reactor, which comprises adding resorcinol, an inorganic salt, and an organic solvent having a solubility parameter of 7.0 to 12.5 to a water solvent, stirring the mixture to give a two-phase system containing no remaining solid matter, adding an acid catalyst, adding formalin dropwise into the reaction system to cause a liquid-liquid heterogeneous reaction to proceed, removing the aqueous layer, adding an organic solvent and water to the reaction product layer, the amount of the water being half of the amount of the organic solvent, stirring the resulting mixture, allowing it to stand, and then removing the aqueous layer to obtain the resorcinol-formalin resin.