A micellar water-based composition containing a chitosan derivative having hydrophilic and hydrophobic groups incorporated therein and a steroid compound; and a method for solubilizing a steroid compound which comprises adding a chitosan derivative having hydrophilic and hydrophobic groups incorporated therein to an aqueous medium together with the steroid compound to form a micellar water-based composition. The steroid compound thus solubilized permits a water-insoluble drug which has been incapable of injection because of its water insolubility to be used as a parenteral solution and serves to accelerate the absorption of a drug which, when used as peroral preparations, has had poor absorbability because of its poor solubility.
