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 (A) is a polyethylene oxide represented by formula (II)

        HO-(CH 2 CH 2 O) 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 C 15-24 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-R 2 -N=C=O     (IV)

wherein R 2 represents methyldiphenylene, hexamethylene, methyldicyclohexylene, 3-methyl-3,5,5-trimethylcyclohexylene, dimethylphenylene, or tolylene.