A method of producing silica-based fine particles comprising the following steps: (a) a step of preparing a dispersion liquid of primary particles of composite oxide with an average diameter (D p1) in a range from 3 to 300 nm, the step comprising simultaneously adding an aqueous silicate solution and/or an acidic silicic acid solution and an aqueous solution of an alkali-soluble inorganic compound into an alkali aqueous solution or into an alkali aqueous solution with seed particles dispersed therein, wherein a molar ratio of MO x /SiO 2 is in a range from 0.01 to 2, herein MO x denotes an inorganic oxide other than silica, and SiO 2 denotes silica, (b) a step of preparing a dispersion liquid of secondary particles of composite oxide with an average diameters (D p2) of up to 500 nm, the step comprising adding an aqueous silicate solution and/or an acidic silicic acid solution and an aqueous solution of alkali-soluble inorganic compound into the dispersion liquid prepared in the step (a), wherein a molar ratio MO x /SiO 2 is smaller than that employed in the step (a) above, wherein a value of B/A (A: the molar ratio MO x /SiO 2 in step (a), B: the molar ratio MO x /SiO 2 in step (b)) is 0.8 or below, (c) a step of preparing a dispersion liquid of silica-based fine particles, the step comprising adding an acid to the dispersion liquid of secondary particles so that at least a portion of chemical elements constituting the secondary particles other than silicon is removed, (d) optionally, a step of forming a silica-coating layer on the silica-based fine particles by adding an organic silicon compound expressed by the following chemical formula and/or a partially hydrolyzed product thereof, and an alkali aqueous solution, if necessary, into the dispersion liquid of silica-based fine particles obtained in the step (c) above: R n SiX (4-n) wherein R denotes a not-substituted or substituted hydrocarbon group having 1 to 10 carbon atoms, an acrylic group, an epoxy group, a methacrylic group, amino group, or a CF 3 group; X denotes an alkoxy group having 1 to 4 carbon atoms, a silanol group, a halogen or hydrogen; and n indicates an integral number in the range from 0 to 3, and (e) a step of aging the dispersion liquid of silica-based fine particles at a temperature ranging from a room temperature to 300°C, wherein cleaning is performed prior to the aging, wherein the average diameter of the silica-based fine particles is in a range from 5 to 500 nm. (a) a step of preparing a dispersion liquid of primary particles of composite oxide with an average diameter (D p1) in a range from 3 to 300 nm, the step comprising simultaneously adding an aqueous silicate solution and/or an acidic silicic acid solution and an aqueous solution of an alkali-soluble inorganic compound into an alkali aqueous solution or into an alkali aqueous solution with seed particles dispersed therein, wherein a molar ratio of MO x /SiO 2 is in a range from 0.01 to 2, herein MO x denotes an inorganic oxide other than silica, and SiO 2 denotes silica, (b) a step of preparing a dispersion liquid of secondary particles of composite oxide with an average diameters (D p2) of up to 500 nm, the step comprising adding an aqueous silicate solution and/or an acidic silicic acid solution and an aqueous solution of alkali-soluble inorganic compound into the dispersion liquid prepared in the step (a), wherein a molar ratio MO x /SiO 2 is smaller than that employed in the step (a) above, wherein a value of B/A (A: the molar ratio MO x /SiO 2 in step (a), B: the molar ratio MO x /SiO 2 in step (b)) is 0.8 or below, (c) a step of preparing a dispersion liquid of silica-based fine particles, the step comprising adding an acid to the dispersion liquid of secondary particles so that at least a portion of chemical elements constituting the secondary particles other than silicon is removed, (d) optionally, a step of forming a silica-coating layer on the silica-based fine particles by adding an organic silicon compound expressed by the following chemical formula and/or a partially hydrolyzed product thereof, and an alkali aqueous solution, if necessary, into the dispersion liquid of silica-based fine particles obtained in the step (c) above: R n SiX (4-n) wherein R denotes a not-substituted or substituted hydrocarbon group having 1 to 10 carbon atoms, an acrylic group, an epoxy group, a methacrylic group, amino group, or a CF 3 group; X denotes an alkoxy group having 1 to 4 carbon atoms, a silanol group, a halogen or hydrogen; and n indicates an integral number in the range from 0 to 3, and (e) a step of aging the dispersion liquid of silica-based fine particles at a temperature ranging from a room temperature to 300°C, wherein cleaning is performed prior to the aging, wherein the average diameter of the silica-based fine particles is in a range from 5 to 500 nm.