A method for producing a purified active silicic acid solution fulfilling the condition: an existing amount of plate-like fine particles having a length of one side of 0.2 to 4.0 μm and a thickness of 1 to 100 nm is measured to be 0% to 30% in accordance with measuring method A below, the method characterized by comprising the steps of: preparing an active silicic acid solution by subjecting an alkali silicate aqueous solution having a silica concentration of 0.5% by mass to 10.0% by mass to cation-exchange to remove alkaline components; and filtering the active silicic acid solution through a filter whose removal rate of particles having a primary particle size of 1.0 μm is 50% or more, and whose filtering rate is 13 L/min to 400 L/min per 1 m 2 of the filtration area of the used filter, measuring method A: when a membrane-type filter (filtration area: 4.90 cm 2) having an absolute pore size of 0.4 μm through which 30 mL of a solution to be observed having a silica concentration of 4% by mass and a temperature of 25°C is passed, is observed under a scanning electron microscope by being magnified by 5,000 times, a state in which one or more of the plate-like fine particles exist within one visual field as an observation area of a rectangle having a length of 15 μm and a width of 20 μm is measured as one count, and the presence or absence of the count is determined with respect to all of 100 visual fields having visual field areas that do not overlap with each other to measure the obtained total number of counts as the existing amount (%) of the plate-like fine particles. an existing amount of plate-like fine particles having a length of one side of 0.2 to 4.0 μm and a thickness of 1 to 100 nm is measured to be 0% to 30% in accordance with measuring method A below, the method characterized by comprising the steps of: preparing an active silicic acid solution by subjecting an alkali silicate aqueous solution having a silica concentration of 0.5% by mass to 10.0% by mass to cation-exchange to remove alkaline components; and filtering the active silicic acid solution through a filter whose removal rate of particles having a primary particle size of 1.0 μm is 50% or more, and whose filtering rate is 13 L/min to 400 L/min per 1 m 2 of the filtration area of the used filter, measuring method A: when a membrane-type filter (filtration area: 4.90 cm 2) having an absolute pore size of 0.4 μm through which 30 mL of a solution to be observed having a silica concentration of 4% by mass and a temperature of 25°C is passed, is observed under a scanning electron microscope by being magnified by 5,000 times, a state in which one or more of the plate-like fine particles exist within one visual field as an observation area of a rectangle having a length of 15 μm and a width of 20 μm is measured as one count, and the presence or absence of the count is determined with respect to all of 100 visual fields having visual field areas that do not overlap with each other to measure the obtained total number of counts as the existing amount (%) of the plate-like fine particles. preparing an active silicic acid solution by subjecting an alkali silicate aqueous solution having a silica concentration of 0.5% by mass to 10.0% by mass to cation-exchange to remove alkaline components; and filtering the active silicic acid solution through a filter whose removal rate of particles having a primary particle size of 1.0 μm is 50% or more, and whose filtering rate is 13 L/min to 400 L/min per 1 m 2 of the filtration area of the used filter, measuring method A: when a membrane-type filter (filtration area: 4.90 cm 2) having an absolute pore size of 0.4 μm through which 30 mL of a solution to be observed having a silica concentration of 4% by mass and a temperature of 25°C is passed, is observed under a scanning electron microscope by being magnified by 5,000 times, a state in which one or more of the plate-like fine particles exist within one visual field as an observation area of a rectangle having a length of 15 μm and a width of 20 μm is measured as one count, and the presence or absence of the count is determined with respect to all of 100 visual fields having visual field areas that do not overlap with each other to measure the obtained total number of counts as the existing amount (%) of the plate-like fine particles.