An organic thin film forming method for forming an organic thin film on a substrate surface comprising: obtaining an auxiliary agent by mixing a metal surfactant having at least one hydrolytic group and a compound capable of interacting with the metal surfactant, obtaining a solution for forming the organic thin film by the auxiliary agent and a metal surfactant having at least one hydrolytic group, in an organic solvent, and contacting the substrate with the solution for forming the organic thin film; wherein, the solution for forming the organic thin film in which the moisture content has been adjusted or maintained to 50 to 1000 ppm is used, the metal surfactant is a compound represented by formula: R 1 n MX m-n (wherein, R 1 represents an optionally substituted hydrocarbon group having 10 to 30 carbon atoms, an optionally substituted halogenated hydrocarbon group having 10 to 30 carbon atoms, a hydrocarbon group containing a linking group, or a halogenated hydrocarbon group containing a linking group, M represents a silicon atom, X represents a hydroxyl group or a hydrolytic group, m represents the valence of M, n represents 1, and X may be the same or different when (m-n) is 2 or more), the compound capable of interacting with the metal surfactant is at least one type selected from the group consisting of a metal oxide, a metal alkoxide, a partial hydrolysis product of a metal alkoxide, a silanol condensation catalyst and an acid catalyst, the metal of the metal alkoxide or the partial hydrolysis product of the metal alkoxide is at least one type selected from the group consisting of titanium, zirconium, aluminum, silicon, germanium, indium, tin, tantalum, zinc, tungsten and lead, and the metal surfactant is a compound represented by formula: R 11 n1 M 1 X 1 m1-n1 (wherein, R 11 represents an optionally substituted hydrocarbon group, an optionally substituted halogenated hydrocarbon group, a hydrocarbon group containing a linking group, or a halogenated hydrocarbon group containing a linking group, M 1 represents a silicon atom, X 1 represents a hydroxyl group or a hydrolytic group, m 1 represents the valence of M, n 1 represents 1, and X 1 may be the same or different when (m 1 -n 1) is 2 or more). obtaining an auxiliary agent by mixing a metal surfactant having at least one hydrolytic group and a compound capable of interacting with the metal surfactant, obtaining a solution for forming the organic thin film by the auxiliary agent and a metal surfactant having at least one hydrolytic group, in an organic solvent, and contacting the substrate with the solution for forming the organic thin film; wherein, the solution for forming the organic thin film in which the moisture content has been adjusted or maintained to 50 to 1000 ppm is used, the metal surfactant is a compound represented by formula: R 1 n MX m-n (wherein, R 1 represents an optionally substituted hydrocarbon group having 10 to 30 carbon atoms, an optionally substituted halogenated hydrocarbon group having 10 to 30 carbon atoms, a hydrocarbon group containing a linking group, or a halogenated hydrocarbon group containing a linking group, M represents a silicon atom, X represents a hydroxyl group or a hydrolytic group, m represents the valence of M, n represents 1, and X may be the same or different when (m-n) is 2 or more), (wherein, R 1 represents an optionally substituted hydrocarbon group having 10 to 30 carbon atoms, an optionally substituted halogenated hydrocarbon group having 10 to 30 carbon atoms, a hydrocarbon group containing a linking group, or a halogenated hydrocarbon group containing a linking group, M represents a silicon atom, X represents a hydroxyl group or a hydrolytic group, m represents the valence of M, n represents 1, and X may be the same or different when (m-n) is 2 or more), the compound capable of interacting with the metal surfactant is at least one type selected from the group consisting of a metal oxide, a metal alkoxide, a partial hydrolysis product of a metal alkoxide, a silanol condensation catalyst and an acid catalyst, the metal of the metal alkoxide or the partial hydrolysis product of the metal alkoxide is at least one type selected from the group consisting of titanium, zirconium, aluminum, silicon, germanium, indium, tin, tantalum, zinc, tungsten and lead, and the metal surfactant is a compound represented by formula: R 11 n1 M 1 X 1 m1-n1 (wherein, R 11 represents an optionally substituted hydrocarbon group, an optionally substituted halogenated hydrocarbon group, a hydrocarbon group containing a linking group, or a halogenated hydrocarbon group containing a linking group, M 1 represents a silicon atom, X 1 represents a hydroxyl group or a hydrolytic group, m 1 represents the valence of M, n 1 represents 1, and X 1 may be the same or different when (m 1 -n 1) is 2 or more). (wherein, R 11 represents an optionally substituted hydrocarbon group, an optionally substituted halogenated hydrocarbon group, a hydrocarbon group containing a linking group, or a halogenated hydrocarbon group containing a linking group, M 1 represents a silicon atom, X 1 represents a hydroxyl group or a hydrolytic group, m 1 represents the valence of M, n 1 represents 1, and X 1 may be the same or different when (m 1 -n 1) is 2 or more).