A purification method of polyoxyalkylene derivative, wherein an impurity is separated from a polyoxyalkylene derivative having a molecular weight of 8,800 to 100,000 (measured by gel permeation chromatography under the conditions as detailed in the experimental part of the description) represented by the following general formula, the impurity being different from the polyoxyalkylene derivative in the number of hydroxyl groups, the method comprising the following steps,,, and: step: a step in which an aprotic organic solvent is used in an amount at least 5 times by weight the amount of the polyoxyalkylene derivative to dissolve the polyoxyalkylene derivative to give a solution of the polyoxyalkylene derivative; step: a step in which an inorganic adsorbent comprising an oxide containing at least one of aluminum and silicon is added to the solution in an amount 0.5 to 5 times by weight the amount of the polyoxyalkylene derivative to produce a slurry; step: a step in which the slurry is stirred at 25°C or higher; and step: a step in which the polyoxyalkylene derivative is recovered from the slurry: wherein Z is a residue of a compound having 2 to 8 active hydrogen atoms; Y 1 and Y 2 represent an ether bond, a thioether bond, an ester bond, a urethane bond, an amide bond, a carbonate bond, a secondary amino group, or an alkylene group containing any of these; Polymer 1 and Polymer 2 represent a linear or branched polyoxyalkylene chain comprised of oxyalkylene groups having 2 to 4 carbon atoms; R represents a hydrocarbon group having 1 to 7 carbon atoms or an acetal group having 3 to 9 carbon atoms; X represents an amino group, a protected amino group, a protected carboxyl group, an aldehyde group, a protected aldehyde group, a hydroxyl group, a protected hydroxyl group, a thiol group, a protected thiol group, a sulfonyl group, a vinyl group, an allyl group, a cyano group, or an alkylene group containing any of these, or a hydrogen atom; m and n are such that m=1 or 0, n=1 or 0, and 1≤m+n; a and b are integers satisfying 0≤a≤8, 0≤b≤8, and 2≤a+b≤8; and when a, and b are integers of 2 or larger, Y 1 and Y 2, Polymer 1 and Polymer 2, R, X, m, and n may be the same or different in the molecule. step: a step in which an aprotic organic solvent is used in an amount at least 5 times by weight the amount of the polyoxyalkylene derivative to dissolve the polyoxyalkylene derivative to give a solution of the polyoxyalkylene derivative; step: a step in which an inorganic adsorbent comprising an oxide containing at least one of aluminum and silicon is added to the solution in an amount 0.5 to 5 times by weight the amount of the polyoxyalkylene derivative to produce a slurry; step: a step in which the slurry is stirred at 25°C or higher; and step: a step in which the polyoxyalkylene derivative is recovered from the slurry: wherein Z is a residue of a compound having 2 to 8 active hydrogen atoms; Y 1 and Y 2 represent an ether bond, a thioether bond, an ester bond, a urethane bond, an amide bond, a carbonate bond, a secondary amino group, or an alkylene group containing any of these; Polymer 1 and Polymer 2 represent a linear or branched polyoxyalkylene chain comprised of oxyalkylene groups having 2 to 4 carbon atoms; R represents a hydrocarbon group having 1 to 7 carbon atoms or an acetal group having 3 to 9 carbon atoms; X represents an amino group, a protected amino group, a protected carboxyl group, an aldehyde group, a protected aldehyde group, a hydroxyl group, a protected hydroxyl group, a thiol group, a protected thiol group, a sulfonyl group, a vinyl group, an allyl group, a cyano group, or an alkylene group containing any of these, or a hydrogen atom; m and n are such that m=1 or 0, n=1 or 0, and 1≤m+n; a and b are integers satisfying 0≤a≤8, 0≤b≤8, and 2≤a+b≤8; and when a, and b are integers of 2 or larger, Y 1 and Y 2, Polymer 1 and Polymer 2, R, X, m, and n may be the same or different in the molecule.