The object of the present invention is to provide a modified polyalkylene oxide capable of yielding an aqueous solution excellent in transparency with high viscosity, even when combined with a cationic surfactant. The present invention provides a modified polyalkylene oxide obtained by reacting a polyalkylene oxide compound (A), a polyether monohydric alcohol (B), and a diisocyanate compound (C); wherein W is a polyethylene oxide represented by formula (II) HO—(CH2CH2O)n—H  (II) wherein n is an integer of 130 to 680; wherein (B) comprises a random copolymer of ethylene oxide and propylene oxide, the random copolymer having a hydroxy group at one terminal and a linear-chain C15-24 alkyl group at the other terminal, and having a ratio (a/b) of 1 to 2 wherein a represents the number of moles of ethylene oxide added and b represents the number of moles of propylene oxide added; and wherein (C) is at least one member selected from the group consisting of compounds represented by formula (IV) O═C═N—R2—N═C═O  (IV) wherein R2 represents methyldiphenylene, hexamethylene, methyldicyclohexylene, 3-methyl-3,5,5-trimethylcyclohexylene, dimethylphenylene, or tolylene.