A method for measuring an amount of a water-absorbing resin included in a hygienic material, an absorbent article, or an intermediate product in a manufacturing process thereof, wherein the water-absorbing resin includes a water-soluble cation derived from neutralization of an acid group of the water-absorbing resin, the method comprising: A) a step for measuring an amount of a predetermined water-soluble cation in a reference sample including a known amount of the water-absorbing resin and creating a calibration curve indicating a relation between the amount of the water-absorbing resin and the amount of the predetermined water-soluble cation in the reference sample on the basis of the obtained measurement result; B) a step for measuring an amount of the predetermined water-soluble cation in a measurement sample, which includes a portion including the water-absorbing resin, of the hygienic material, the absorbent article, or the intermediate product in the manufacturing process thereof; and C) a step for calculating an amount of the water-absorbing resin in the measurement sample by the calibration curve created in the step A) from the amount of the predetermined water-soluble cation measured in the step B), the step A) and the step B) including measuring the amount of the predetermined water-soluble cation using an ion selective electrode method and including the following steps M1) and M2): M1) a step for immersing a sample in an aqueous solution including a total ionic strength adjusting agent (pre-processing step); and M2) a step for measuring the amount of the predetermined water-soluble cation in a pre-processed supernatant liquid obtained in the step M1), wherein the water-soluble cation is selected from a sodium ion, a potassium ion and an ammonium ion, and wherein the total ionic strength adjusting agent is selected from a potassium salt, a calcium salt, a magnesium salt and an ammonium salt when the water-soluble cation is a sodium ion; the total ionic strength adjusting agent is selected from a sodium salt, a calcium salt, a magnesium salt and an ammonium salt when the water-soluble cation is a potassium ion; and the total ionic strength adjusting agent is selected from a sodium salt, a potassium salt, a calcium salt and a magnesium salt when the water-soluble cation is an ammonium ion. A) a step for measuring an amount of a predetermined water-soluble cation in a reference sample including a known amount of the water-absorbing resin and creating a calibration curve indicating a relation between the amount of the water-absorbing resin and the amount of the predetermined water-soluble cation in the reference sample on the basis of the obtained measurement result; B) a step for measuring an amount of the predetermined water-soluble cation in a measurement sample, which includes a portion including the water-absorbing resin, of the hygienic material, the absorbent article, or the intermediate product in the manufacturing process thereof; and C) a step for calculating an amount of the water-absorbing resin in the measurement sample by the calibration curve created in the step A) from the amount of the predetermined water-soluble cation measured in the step B), the step A) and the step B) including measuring the amount of the predetermined water-soluble cation using an ion selective electrode method and including the following steps M1) and M2): M1) a step for immersing a sample in an aqueous solution including a total ionic strength adjusting agent (pre-processing step); and M2) a step for measuring the amount of the predetermined water-soluble cation in a pre-processed supernatant liquid obtained in the step M1), M1) a step for immersing a sample in an aqueous solution including a total ionic strength adjusting agent (pre-processing step); and M2) a step for measuring the amount of the predetermined water-soluble cation in a pre-processed supernatant liquid obtained in the step M1), wherein the water-soluble cation is selected from a sodium ion, a potassium ion and an ammonium ion, and wherein the total ionic strength adjusting agent is selected from a potassium salt, a calcium salt, a magnesium salt and an ammonium salt when the water-soluble cation is a sodium ion; the total ionic strength adjusting agent is selected from a sodium salt, a calcium salt, a magnesium salt and an ammonium salt when the water-soluble cation is a potassium ion; and the total ionic strength adjusting agent is selected from a sodium salt, a potassium salt, a calcium salt and a magnesium salt when the water-soluble cation is an ammonium ion.