A aqueous modified polyisocyanate intended to be dispersed in an aqueous medium for use and obtained by reacting an HDI derivative with (A) a modifying agent composed of a methoxy polyoxyalkylene glycol mainly comprising an ethylene oxide unit, (B) a modifying agent composed of a hydroxyl group-terminated polyoxyalkylene glycol produced by using an alcohol having 8 or more carbon atoms as an initiator and mainly comprising a propylene oxide unit, and (C) a modifying agent composed of an ester compound having at least one hydroxyl group with an alkali metal salt of sulfonic acid introduced therein, wherein the concentration (calculated value) of the alkali metal salt of sulfonic acid derived from the modifying agent (C) is 1.5 to 25 μmol/g.The aqueous modified polyisocyanate is not only excellent in dispersion stability in water but also excellent in stability of the isocyanate group in water even under temperature conditions of 35 ° C. or higher.